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Machine

A machine is a physical system that uses power to apply forces and control movement to perform an action. The term is commonly applied to artificial devices, such as those employing engines or motors, but also to natural biological macromolecules, such as molecular machines. Machines can be driven by animals and people, by natural forces such as wind and water, and by chemical, thermal, or electrical power, and include a system of mechanisms that shape the actuator input to achieve a specific application of output forces and movement. They can also include computers and sensors that monitor performance and plan movement, often called mechanical systems.

Renaissance natural philosophers identified six simple machines which were the elementary devices that put a load into motion, and calculated the ratio of output force to input force, known today as mechanical advantage.

Modern machines are complex systems that consist of structural elements, mechanisms and control components and include interfaces for convenient use. Examples include: a wide range of vehicles, such as trains, automobiles, boats and airplanes; appliances in the home and office, including computers, building air handling and water handling systems; as well as farm machinery, machine tools and factory automation systems and robots.

Etymology
The English word machine comes through Middle French from Latin machina, which in turn derives from the Greek (Doric μαχανά, Ionic μηχανή 'contrivance, machine, engine', a derivation from μῆχος  'means, expedient, remedy' ). The word mechanical (Greek: μηχανικός) comes from the same Greek roots. A wider meaning of 'fabric, structure' is found in classical Latin, but not in Greek usage. This meaning is found in late medieval French, and is adopted from the French into English in the mid-16th century.

In the 17th century, the word machine could also mean a scheme or plot, a meaning now expressed by the derived machination. The modern meaning develops out of specialized application of the term to stage engines used in theater and to military siege engines, both in the late 16th and early 17th centuries. The OED traces the formal, modern meaning to John Harris' Lexicon Technicum (1704), which has:

 * Machine, or Engine, in Mechanicks, is whatsoever hath Force sufficient either to raise or stop the Motion of a Body. Simple Machines are commonly reckoned to be Six in Number, viz. the Ballance, Leaver, Pulley, Wheel, Wedge, and Screw. Compound Machines, or Engines, are innumerable.

The word engine used as a (near-) synonym both by Harris and in later language derives ultimately (via Old French) from Latin ingenium 'ingenuity, an invention'.

History
The hand axe, made by chipping flint to form a wedge, in the hands of a human transforms force and movement of the tool into a transverse splitting forces and movement of the workpiece. The hand axe is the first example of a wedge, the oldest of the six classic simple machines, from which most machines are based. The second oldest simple machine was the inclined plane (ramp), which has been used since prehistoric times to move heavy objects.

The other four simple machines were invented in the ancient Near East. The wheel, along with the wheel and axle mechanism, was invented in Mesopotamia (modern Iraq) during the 5th millennium BC. The lever mechanism first appeared around 5,000 years ago in the Near East, where it was used in a simple balance scale, and to move large objects in ancient Egyptian technology. The lever was also used in the shadoof water-lifting device, the first crane machine, which appeared in Mesopotamia c. 3000 BC, and then in ancient Egyptian technology c. 2000 BC. The earliest evidence of pulleys date back to Mesopotamia in the early 2nd millennium BC, and ancient Egypt during the Twelfth Dynasty (1991-1802 BC). The screw, the last of the simple machines to be invented, first appeared in Mesopotamia during the Neo-Assyrian period (911-609) BC. The Egyptian pyramids were built using three of the six simple machines, the inclined plane, the wedge, and the lever.

Three of the simple machines were studied and described by Greek philosopher Archimedes around the 3rd century BC: the lever, pulley and screw. Archimedes discovered the principle of mechanical advantage in the lever. Later Greek philosophers defined the classic five simple machines (excluding the inclined plane) and were able to roughly calculate their mechanical advantage. Hero of Alexandria (c. 10–75 AD) in his work Mechanics lists five mechanisms that can "set a load in motion"; lever, windlass, pulley, wedge, and screw, and describes their fabrication and uses. However, the Greeks' understanding was limited to statics (the balance of forces) and did not include dynamics (the tradeoff between force and distance) or the concept of work.

The earliest practical wind-powered machines, the windmill and wind pump, first appeared in the Muslim world during the Islamic Golden Age, in what are now Iran, Afghanistan, and Pakistan, by the 9th century AD. The earliest practical steam-powered machine was a steam jack driven by a steam turbine, described in 1551 by Taqi ad-Din Muhammad ibn Ma'ruf in Ottoman Egypt.

The cotton gin was invented in India by the 6th century AD, and the spinning wheel was invented in the Islamic world by the early 11th century, both of which were fundamental to the growth of the cotton industry. The spinning wheel was also a precursor to the spinning jenny.

The earliest programmable machines were developed in the Muslim world. A music sequencer, a programmable musical instrument, was the earliest type of programmable machine. The first music sequencer was an automated flute player invented by the Banu Musa brothers, described in their Book of Ingenious Devices, in the 9th century. In 1206, Al-Jazari invented programmable automata/robots. He described four automaton musicians, including drummers operated by a programmable drum machine, where they could be made to play different rhythms and different drum patterns.

During the Renaissance, the dynamics of the Mechanical Powers, as the simple machines were called, began to be studied from the standpoint of how much useful work they could perform, leading eventually to the new concept of mechanical work. In 1586 Flemish engineer Simon Stevin derived the mechanical advantage of the inclined plane, and it was included with the other simple machines. The complete dynamic theory of simple machines was worked out by Italian scientist Galileo Galilei in 1600 in Le Meccaniche ("On Mechanics"). He was the first to understand that simple machines do not create energy, they merely transform it.

The classic rules of sliding friction in machines were discovered by Leonardo da Vinci (1452–1519), but remained unpublished in his notebooks. They were rediscovered by Guillaume Amontons (1699) and were further developed by Charles-Augustin de Coulomb (1785).

James Watt patented his parallel motion linkage in 1782, which made the double acting steam engine practical. The Boulton and Watt steam engine and later designs powered steam locomotives, steam ships, and factories.

The Industrial Revolution was a period from 1750 to 1850 where changes in agriculture, manufacturing, mining, transportation, and technology had a profound effect on the social, economic and cultural conditions of the times. It began in the United Kingdom, then subsequently spread throughout Western Europe, North America, Japan, and eventually the rest of the world.

Starting in the later part of the 18th century, there began a transition in parts of Great Britain's previously manual labour and draft-animal-based economy towards machine-based manufacturing. It started with the mechanisation of the textile industries, the development of iron-making techniques and the increased use of refined coal.

Simple machines

The idea that a machine can be decomposed into simple movable elements led Archimedes to define the lever, pulley and screw as simple machines. By the time of the Renaissance this list increased to include the wheel and axle, wedge and inclined plane. The modern approach to characterizing machines focusses on the components that allow movement, known as joints.

Wedge (hand axe): Perhaps the first example of a device designed to manage power is the hand axe, also called biface and Olorgesailie. A hand axe is made by chipping stone, generally flint, to form a bifacial edge, or wedge. A wedge is a simple machine that transforms lateral force and movement of the tool into a transverse splitting force and movement of the workpiece. The available power is limited by the effort of the person using the tool, but because power is the product of force and movement, the wedge amplifies the force by reducing the movement. This amplification, or mechanical advantage is the ratio of the input speed to output speed. For a wedge this is given by 1/tanα, where α is the tip angle. The faces of a wedge are modeled as straight lines to form a sliding or prismatic joint.

Lever: The lever is another important and simple device for managing power. This is a body that pivots on a fulcrum. Because the velocity of a point farther from the pivot is greater than the velocity of a point near the pivot, forces applied far from the pivot are amplified near the pivot by the associated decrease in speed. If a is the distance from the pivot to the point where the input force is applied and b is the distance to the point where the output force is applied, then a/b is the mechanical advantage of the lever. The fulcrum of a lever is modeled as a hinged or revolute joint.

Wheel: The wheel is an important early machine, such as the chariot. A wheel uses the law of the lever to reduce the force needed to overcome friction when pulling a load. To see this notice that the friction associated with pulling a load on the ground is approximately the same as the friction in a simple bearing that supports the load on the axle of a wheel. However, the wheel forms a lever that magnifies the pulling force so that it overcomes the frictional resistance in the bearing.

The classification of simple machines to provide a strategy for the design of new machines was developed by Franz Reuleaux, who collected and studied over 800 elementary machines. He recognized that the classical simple machines can be separated into the lever, pulley and wheel and axle that are formed by a body rotating about a hinge, and the inclined plane, wedge and screw that are similarly a block sliding on a flat surface.

Simple machines are elementary examples of kinematic chains or linkages that are used to model mechanical systems ranging from the steam engine to robot manipulators. The bearings that form the fulcrum of a lever and that allow the wheel and axle and pulleys to rotate are examples of a kinematic pair called a hinged joint. Similarly, the flat surface of an inclined plane and wedge are examples of the kinematic pair called a sliding joint. The screw is usually identified as its own kinematic pair called a helical joint.

This realization shows that it is the joints, or the connections that provide movement, that are the primary elements of a machine. Starting with four types of joints, the rotary joint, sliding joint, cam joint and gear joint, and related connections such as cables and belts, it is possible to understand a machine as an assembly of solid parts that connect these joints called a mechanism.

Two levers, or cranks, are combined into a planar four-bar linkage by attaching a link that connects the output of one crank to the input of another. Additional links can be attached to form a six-bar linkage or in series to form a robot.

Mechanical systems
A mechanical system manages power to accomplish a task that involves forces and movement. Modern machines are systems consisting of (i) a power source and actuators that generate forces and movement, (ii) a system of mechanisms that shape the actuator input to achieve a specific application of output forces and movement, (iii) a controller with sensors that compare the output to a performance goal and then directs the actuator input, and (iv) an interface to an operator consisting of levers, switches, and displays. This can be seen in Watt's steam engine in which the power is provided by steam expanding to drive the piston. The walking beam, coupler and crank transform the linear movement of the piston into rotation of the output pulley. Finally, the pulley rotation drives the flyball governor which controls the valve for the steam input to the piston cylinder.

The adjective "mechanical" refers to skill in the practical application of an art or science, as well as relating to or caused by movement, physical forces, properties or agents such as is dealt with by mechanics. Similarly Merriam-Webster Dictionary defines "mechanical" as relating to machinery or tools.

Power flow through a machine provides a way to understand the performance of devices ranging from levers and gear trains to automobiles and robotic systems. The German mechanician Franz Reuleaux wrote, "a machine is a combination of resistant bodies so arranged that by their means the mechanical forces of nature can be compelled to do work accompanied by certain determinate motion." Notice that forces and motion combine to define power.

More recently, Uicker et al. stated that a machine is "a device for applying power or changing its direction."McCarthy and Soh describe a machine as a system that "generally consists of a power source and a mechanism for the controlled use of this power."

Power sources
Human and animal effort were the original power sources for early machines.

Waterwheel: Waterwheels appeared around the world around 300 BC to use flowing water to generate rotary motion, which was applied to milling grain, and powering lumber, machining and textile operations. Modern water turbines use water flowing through a dam to drive an electric generator.

Windmill: Early windmills captured wind power to generate rotary motion for milling operations. Modern wind turbines also drives a generator. This electricity in turn is used to drive motors forming the actuators of mechanical systems.

Engine: The word engine derives from "ingenuity" and originally referred to contrivances that may or may not be physical devices. A steam engine uses heat to boil water contained in a pressure vessel; the expanding steam drives a piston or a turbine. This principle can be seen in the aeolipile of Hero of Alexandria. This is called an external combustion engine.

An automobile engine is called an internal combustion engine because it burns fuel (an exothermic chemical reaction) inside a cylinder and uses the expanding gases to drive a piston. A jet engine uses a turbine to compress air which is burned with fuel so that it expands through a nozzle to provide thrust to an aircraft, and so is also an "internal combustion engine."

Power plant: The heat from coal and natural gas combustion in a boiler generates steam that drives a steam turbine to rotate an electric generator. A nuclear power plant uses heat from a nuclear reactor to generate steam and electric power. This power is distributed through a network of transmission lines for industrial and individual use.

Motors: Electric motors use either AC or DC electric current to generate rotational movement. Electric servomotors are the actuators for mechanical systems ranging from robotic systems to modern aircraft.

Fluid Power: Hydraulic and pneumatic systems use electrically driven pumps to drive water or air respectively into cylinders to power linear movement.

Electrochemical: Chemicals and materials can also be sources of power. They may chemically deplete or need re-charging, as is the case with batteries, or they may produce power without changing their state, which is the case for solar cells and thermoelectric generators. All of these, however, still require their energy to come from elsewhere. With batteries, it is the already existing chemical potential energy inside. In solar cells and thermoelectrics, the energy source is light and heat respectively.

Mechanisms
The mechanism of a mechanical system is assembled from components called machine elements. These elements provide structure for the system and control its movement.

The structural components are, generally, the frame members, bearings, splines, springs, seals, fasteners and covers. The shape, texture and color of covers provide a styling and operational interface between the mechanical system and its users.

The assemblies that control movement are also called "mechanisms." Mechanisms are generally classified as gears and gear trains, which includes belt drives and chain drives, cam and follower mechanisms, and linkages, though there are other special mechanisms such as clamping linkages, indexing mechanisms, escapements and friction devices such as brakes and clutches.

The number of degrees of freedom of a mechanism, or its mobility, depends on the number of links and joints and the types of joints used to construct the mechanism. The general mobility of a mechanism is the difference between the unconstrained freedom of the links and the number of constraints imposed by the joints. It is described by the Chebychev–Grübler–Kutzbach criterion.

Gears and gear trains
The transmission of rotation between contacting toothed wheels can be traced back to the Antikythera mechanism of Greece and the south-pointing chariot of China. Illustrations by the renaissance scientist Georgius Agricola show gear trains with cylindrical teeth. The implementation of the involute tooth yielded a standard gear design that provides a constant speed ratio. Some important features of gears and gear trains are:
 * The ratio of the pitch circles of mating gears defines the speed ratio and the mechanical advantage of the gear set.
 * A planetary gear train provides high gear reduction in a compact package.
 * It is possible to design gear teeth for gears that are non-circular, yet still transmit torque smoothly.
 * The speed ratios of chain and belt drives are computed in the same way as gear ratios. See bicycle gearing.

Cam and follower mechanisms
A cam and follower is formed by the direct contact of two specially shaped links. The driving link is called the cam (also see cam shaft) and the link that is driven through the direct contact of their surfaces is called the follower. The shape of the contacting surfaces of the cam and follower determines the movement of the mechanism.

Linkages
A linkage is a collection of links connected by joints. Generally, the links are the structural elements and the joints allow movement. Perhaps the single most useful example is the planar four-bar linkage. However, there are many more special linkages:
 * Watt's linkage is a four-bar linkage that generates an approximate straight line. It was critical to the operation of his design for the steam engine. This linkage also appears in vehicle suspensions to prevent side-to-side movement of the body relative to the wheels. Also see the article Parallel motion.
 * The success of Watt's linkage lead to the design of similar approximate straight-line linkages, such as Hoeken's linkage and Chebyshev's linkage.
 * The Peaucellier linkage generates a true straight-line output from a rotary input.
 * The Sarrus linkage is a spatial linkage that generates straight-line movement from a rotary input.
 * The Klann linkage and the Jansen linkage are recent inventions that provide interesting walking movements. They are respectively a six-bar and an eight-bar linkage.

Planar mechanism
A planar mechanism is a mechanical system that is constrained so the trajectories of points in all the bodies of the system lie on planes parallel to a ground plane. The rotational axes of hinged joints that connect the bodies in the system are perpendicular to this ground plane.

Spherical mechanism
A spherical mechanism is a mechanical system in which the bodies move in a way that the trajectories of points in the system lie on concentric spheres. The rotational axes of hinged joints that connect the bodies in the system pass through the center of these circle.

Spatial mechanism
A spatial mechanism is a mechanical system that has at least one body that moves in a way that its point trajectories are general space curves. The rotational axes of hinged joints that connect the bodies in the system form lines in space that do not intersect and have distinct common normals.

Flexure mechanisms
A flexure mechanism consists of a series of rigid bodies connected by compliant elements (also known as flexure joints) that is designed to produce a geometrically well-defined motion upon application of a force.

Machine elements
The elementary mechanical components of a machine are termed machine elements. These elements consist of three basic types (i) structural components such as frame members, bearings, axles, splines, fasteners, seals, and lubricants, (ii) mechanisms that control movement in various ways such as gear trains, belt or chain drives, linkages, cam and follower systems, including brakes and clutches, and (iii) control components such as buttons, switches, indicators, sensors, actuators and computer controllers. While generally not considered to be a machine element, the shape, texture and color of covers are an important part of a machine that provide a styling and operational interface between the mechanical components of a machine and its users.

Structural components
A number of machine elements provide important structural functions such as the frame, bearings, splines, spring and seals.
 * The recognition that the frame of a mechanism is an important machine element changed the name three-bar linkage into four-bar linkage. Frames are generally assembled from truss or beam elements.
 * Bearings are components designed to manage the interface between moving elements and are the source of friction in machines. In general, bearings are designed for pure rotation or straight line movement.
 * Splines and keys are two ways to reliably mount an axle to a wheel, pulley or gear so that torque can be transferred through the connection.
 * Springs provides forces that can either hold components of a machine in place or acts as a suspension to support part of a machine.
 * Seals are used between mating parts of a machine to ensure fluids, such as water, hot gases, or lubricant do not leak between the mating surfaces.
 * Fasteners such as screws, bolts, spring clips, and rivets are critical to the assembly of components of a machine. Fasteners are generally considered to be removable. In contrast, joining methods, such as welding, soldering, crimping and the application of adhesives, usually require cutting the parts to disassemble the components

Controllers
Controllers combine sensors, logic, and actuators to maintain the performance of components of a machine. Perhaps the best known is the flyball governor for a steam engine. Examples of these devices range from a thermostat that as temperature rises opens a valve to cooling water to speed controllers such as the cruise control system in an automobile. The programmable logic controller replaced relays and specialized control mechanisms with a programmable computer. Servomotors that accurately position a shaft in response to an electrical command are the actuators that make robotic systems possible.

Computing machines
Charles Babbage designed machines to tabulate logarithms and other functions in 1837. His Difference engine can be considered an advanced mechanical calculator and his Analytical Engine a forerunner of the modern computer, though none of the larger designs were completed in Babbage's lifetime.

The Arithmometer and the Comptometer are mechanical computers that are precursors to modern digital computers. Models used to study modern computers are termed State machine and Turing machine.

Molecular machines
The biological molecule myosin reacts to ATP and ADP to alternately engage with an actin filament and change its shape in a way that exerts a force, and then disengage to reset its shape, or conformation. This acts as the molecular drive that causes muscle contraction. Similarly the biological molecule kinesin has two sections that alternately engage and disengage with microtubules causing the molecule to move along the microtubule and transport vesicles within the cell, and dynein, which moves cargo inside cells towards the nucleus and produces the axonemal beating of motile cilia and flagella. "In effect, the motile cilium is a nanomachine composed of perhaps over 600 proteins in molecular complexes, many of which also function independently as nanomachines. Flexible linkers allow the mobile protein domains connected by them to recruit their binding partners and induce long-range allostery via protein domain dynamics. " Other biological machines are responsible for energy production, for example ATP synthase which harnesses energy from proton gradients across membranes to drive a turbine-like motion used to synthesise ATP, the energy currency of a cell. Still other machines are responsible for gene expression, including DNA polymerases for replicating DNA, RNA polymerases for producing mRNA, the spliceosome for removing introns, and the ribosome for synthesising proteins. These machines and their nanoscale dynamics are far more complex than any molecular machines that have yet been artificially constructed. These molecules are increasingly considered to be nanomachines.

Researchers have used DNA to construct nano-dimensioned four-bar linkages.

Mechanization and automation
Mechanization (or mechanisation in BE) is providing human operators with machinery that assists them with the muscular requirements of work or displaces muscular work. In some fields, mechanization includes the use of hand tools. In modern usage, such as in engineering or economics, mechanization implies machinery more complex than hand tools and would not include simple devices such as an un-geared horse or donkey mill. Devices that cause speed changes or changes to or from reciprocating to rotary motion, using means such as gears, pulleys or sheaves and belts, shafts, cams and cranks, usually are considered machines. After electrification, when most small machinery was no longer hand powered, mechanization was synonymous with motorized machines.

Automation is the use of control systems and information technologies to reduce the need for human work in the production of goods and services. In the scope of industrialization, automation is a step beyond mechanization. Whereas mechanization provides human operators with machinery to assist them with the muscular requirements of work, automation greatly decreases the need for human sensory and mental requirements as well. Automation plays an increasingly important role in the world economy and in daily experience.

Automata
An automaton (plural: automata or automatons) is a self-operating machine. The word is sometimes used to describe a robot, more specifically an autonomous robot. A Toy Automaton was patented in 1863.

Mechanics
Usher reports that Hero of Alexandria's treatise on Mechanics focussed on the study of lifting heavy weights. Today mechanics refers to the mathematical analysis of the forces and movement of a mechanical system, and consists of the study of the kinematics and dynamics of these systems.

Dynamics of machines
The dynamic analysis of machines begins with a rigid-body model to determine reactions at the bearings, at which point the elasticity effects are included. The rigid-body dynamics studies the movement of systems of interconnected bodies under the action of external forces. The assumption that the bodies are rigid, which means that they do not deform under the action of applied forces, simplifies the analysis by reducing the parameters that describe the configuration of the system to the translation and rotation of reference frames attached to each body.

The dynamics of a rigid body system is defined by its equations of motion, which are derived using either Newtons laws of motion or Lagrangian mechanics. The solution of these equations of motion defines how the configuration of the system of rigid bodies changes as a function of time. The formulation and solution of rigid body dynamics is an important tool in the computer simulation of mechanical systems.

Kinematics of machines
The dynamic analysis of a machine requires the determination of the movement, or kinematics, of its component parts, known as kinematic analysis. The assumption that the system is an assembly of rigid components allows rotational and translational movement to be modeled mathematically as Euclidean, or rigid, transformations. This allows the position, velocity and acceleration of all points in a component to be determined from these properties for a reference point, and the angular position, angular velocity and angular acceleration of the component.

Machine design
Machine design refers to the procedures and techniques used to address the three phases of a machine's lifecycle:
 * 1) invention, which involves the identification of a need, development of requirements, concept generation, prototype development, manufacturing, and verification testing;
 * 2) performance engineering involves enhancing manufacturing efficiency, reducing service and maintenance demands, adding features and improving effectiveness, and validation testing;
 * 3) recycle is the decommissioning and disposal phase and includes recovery and reuse of materials and components.

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Great Plains

The Great Plains are a broad expanse of flatland in North America. The region is located just to the east of the Rocky Mountains, much of it covered in prairie, steppe, and grassland. They are the western part of the Interior Plains, which include the mixed grass prairie, the tallgrass prairie between the Great Lakes and Appalachian Plateau, and the Taiga Plains and Boreal Plains ecozones in Northern Canada. "Great Plains" or Western Plains also describe the ecoregion of the Great Plains, or alternatively the western portion of the Great Plains.

The Great Plains lie across both Central United States and Western Canada, encompassing:
 * Most or all of the U.S. states of Kansas, Nebraska, North Dakota and South Dakota;
 * Eastern parts of the U.S. states of Colorado, Montana, and Wyoming;
 * Parts of the U.S. states of New Mexico, Oklahoma, Texas;
 * Sometimes western parts of Iowa, Minnesota, and Missouri;
 * The southern portions of the Canadian provinces of Alberta, Saskatchewan and Manitoba.

Usage
The term "Great Plains" is used in the United States to describe a sub-section of the even more vast Interior Plains physiographic division, which covers much of the interior of North America. It also has currency as a region of human geography, referring to the Plains Indians or the Plains states.

In Canada the term is rarely used; Natural Resources Canada, the government department responsible for official mapping, treats the Interior Plains as one unit consisting of several related plateaus and plains. There is no region referred to as the "Great Plains" in the Atlas of Canada. In terms of human geography, the term prairie is more commonly used in Canada, and the region is known as the Canadian Prairies, Prairie Provinces or simply "the Prairies".

The North American Environmental Atlas, produced by the Commission for Environmental Cooperation, a North American Free Trade Agreement (NAFTA) agency composed of the geographical agencies of the Mexican, American, and Canadian governments, uses the "Great Plains" as an ecoregion synonymous with predominant prairies and grasslands rather than as physiographic region defined by topography. The Great Plains ecoregion includes five sub-regions: Temperate Prairies, West-Central Semi-Arid Prairies, South-Central Semi-Arid Prairies, Texas Louisiana Coastal Plains, and Tamaulipas-Texas Semi-Arid Plain, which overlap or expand upon other Great Plains designations.

Extent
The region is about 500 mi east to west and 2000 mi north to south. Much of the region was home to American bison herds until they were hunted to near extinction during the mid/late-19th century. It has an area of approximately 1300000 km2. Current thinking regarding the geographic boundaries of the Great Plains is shown by this map at the Center for Great Plains Studies, University of Nebraska–Lincoln. This definition, however, is primarily ecological, not physiographic. The Boreal Plains of Western Canada are physiographically the same, but differentiated by their tundra and forest (rather than grassland) appearance.

The term "Great Plains", for the region west of about the 96th meridian west and east of the Rocky Mountains, was not generally used before the early 20th century. Nevin Fenneman's 1916 study Physiographic Subdivision of the United States brought the term Great Plains into more widespread usage. Before that the region was almost invariably called the High Plains, in contrast to the lower Prairie Plains of the Midwestern states. Today the term "High Plains" is used for a subregion of the Great Plains. The term still remains little-used in Canada compared to the more common, "prairie".

Geography
The Great Plains are the westernmost portion of the vast North American Interior Plains, which extend east to the Appalachian Plateau. The United States Geological Survey divides the Great Plains in the United States into ten physiographic subdivisions:
 * Missouri Coteau or Missouri Plateau (which also extends into Canada), glaciated – east central South Dakota, northern and eastern North Dakota and northeastern Montana;
 * Coteau du Missouri, unglaciated – western South Dakota, northeastern Wyoming, southwestern North Dakota and southeastern Montana;
 * Black Hills – western South Dakota;
 * High Plains – southeastern Wyoming, southwestern South Dakota, western Nebraska (including the Sand Hills), eastern Colorado, western Kansas, western Oklahoma, eastern New Mexico, and northwestern Texas (including the Llano Estacado and Texas Panhandle);
 * Plains Border – central Kansas and northern Oklahoma (including the Flint, Red and Smoky Hills);
 * Colorado Piedmont – eastern Colorado;
 * Raton section – northeastern New Mexico;
 * Pecos Valley – eastern New Mexico;
 * Edwards Plateau – south central Texas; and
 * Central Texas section – central Texas.

Further to this can be added Canadian physiographic sub-regions such as the Alberta Plain, Cypress Hills, Manitoba Escarpment (eastward), Manitoba Plain, Missouri Coteau (shared), Rocky Mountain Foothills (eastward), and Saskatchewan Plain.

The Great Plains consist of a broad stretch of country underlain by nearly horizontal strata extending westward from the 97th meridian west to the base of the Rocky Mountains, a distance of 300 to 500 mi. It extends northward from the Mexican boundary far into Canada. Although the altitude of the plains increases gradually from 600 ft or 1200 ft on the east to 4,000 – or 6000 ft near the mountains, the local relief is generally small. The semi-arid climate excludes tree growth and opens far-reaching views.

The plains are by no means a simple unit. They are of diverse structure and of various stages of erosional development. They are occasionally interrupted by buttes and escarpments. They are frequently broken by valleys. Yet on the whole, a broadly extended surface of moderate relief so often prevails that the name, Great Plains, for the region as a whole is well-deserved.

The western boundary of the plains is usually well-defined by the abrupt ascent of the mountains. The eastern boundary of the plains (in the United States) is more climatic than topographic. The line of 20 in of annual rainfall trends a little east of northward near the 97th meridian. If a boundary must be drawn where nature presents only a gradual transition, this rainfall line may be taken to divide the drier plains from the moister prairies. However, in Canada the eastern boundary of the plains is well defined by the presence of the Canadian Shield to the northeast.

The plains (within the United States) may be described in northern, intermediate, central and southern sections, in relation to certain peculiar features. In Canada, no such division is used: the climatic and vegetation regions are more impactful on human settlement than mere topography, and therefore the region is split into (from north to south), the taiga plains, boreal plains, aspen parkland, and prairie ecoregion regions.

Northern Great Plains

The northern section of the Great Plains, north of latitude 44°, includes eastern Montana, eastern Wyoming, most of North Dakota and South Dakota, southwestern Minnesota and portions of the Canadian provinces including southeastern Alberta, southern Saskatchewan and southwestern Manitoba. The strata here are Cretaceous or early Tertiary, lying nearly horizontal. The surface is shown to be a plain of degradation by a gradual ascent here and there to the crest of a ragged escarpment, the escarpment-remnant of a resistant stratum. There are also the occasional lava-capped mesas and dike formed ridges, surmounting the general level by 500 ft or more and manifestly demonstrating the widespread erosion of the surrounding plains. All these reliefs are more plentiful towards the mountains in central Montana. The peneplain is no longer in the cycle of erosion that witnessed its production. It appears to have suffered a regional uplift or increase in elevation, for the upper Missouri River and its branches no longer flow on the surface of the plain, but in well graded, maturely opened valleys, several hundred feet below the general level. A significant exception to the rule of mature valleys occurs, however, in the case of the Missouri, the largest river, which is broken by several falls on hard sandstones about 50 mi east of the mountains. This peculiar feature is explained as the result of displacement of the river from a better graded preglacial valley by the Pleistocene ice sheet. Here, the ice sheet overspread the plains from the moderately elevated Canadian highlands far on the north-east, instead of from the much higher mountains nearby on the west. The present altitude of the plains near the mountain base is 4000 ft.

The northern plains are interrupted by several small mountain areas. The Black Hills, chiefly in western South Dakota, are the largest group. They rise like a large island from the sea, occupying an oval area of about 100 mi north-south by 50 mi east-west. At Black Elk Peak, they reach an altitude of 7216 ft and have an effective relief over the plains of 2000 or This mountain mass is of flat-arched, dome-like structure, now well dissected by radiating consequent streams. The weaker uppermost strata have been eroded down to the level of the plains where their upturned edges are evenly truncated. The next following harder strata have been sufficiently eroded to disclose the core of underlying igneous and metamorphic crystalline rocks in about half of the domed area.

Intermediate Great Plains
In the intermediate section of the plains, between latitudes 44° and 42°, including southern South Dakota and northern Nebraska, the erosion of certain large districts is peculiarly elaborate. Known as the Badlands, it is a minutely dissected form with a relief of a few hundred feet. This is due to several causes:
 * the dry climate, which prevents the growth of a grassy turf
 * the fine texture of the Tertiary strata in the badland districts
 * every little rill, at times of rain, carves its own little valley.

Central Great Plains
The central section of the Great Plains, between latitudes 42° and 36°, occupying eastern Colorado and western Kansas, is mostly a dissected fluviatile plain. That is, this section was once smoothly covered with a gently sloping plain of gravel and sand that had been spread far forward on a broad denuded area as a piedmont deposit by the rivers which issued from the mountains. Since then, it has been more or less dissected by the erosion of valleys. The central section of the plains thus presents a marked contrast to the northern section.

While the northern section owes its smoothness to the removal of local gravels and sands from a formerly uneven surface by the action of degrading rivers and their inflowing tributaries, the southern section owes its smoothness to the deposition of imported gravels and sands upon a previously uneven surface by the action of aggrading rivers and their outgoing distributaries. The two sections are also alike in that residual eminences still here and there surmount the peneplain of the northern section, while the fluviatile plain of the central section completely buried the pre-existent relief. An exception to this statement must be made for the southwest, close to the mountains in southern Colorado, where some lava-capped mesas (Mesa de Maya, Raton Mesa) stand several thousand feet above the general plain level, and thus testify to the widespread erosion of this region before it was aggraded.

Southern Great Plains
The southern section of the Great Plains, between latitudes 35.5° and 25.5°, lies in western Texas, eastern New Mexico, and western Oklahoma. Like the central section, it is for the most part a dissected fluviatile plain. However, the lower lands which surround it on all sides place it in such strong relief that it stands up as a table-land, known from the time of Mexican occupation as the Llano Estacado. It measures roughly 150 mi east-west and 400 mi north-south. It is of very irregular outline, narrowing to the south. Its altitude is 5500 ft at the highest western point, nearest the mountains whence its gravels were supplied. From there, it slopes southeastward at a decreasing rate, first about 12 ft, then about 7 ft/mi, to its eastern and southern borders, where it is 2000 ft in altitude. Like the High Plains farther north, it is extraordinarily smooth.

It is very dry, except for occasional shallow and temporary water sheets after rains. Llano is separated from the plains on the north by the mature consequent valley of the Canadian River, and from the mountains on the west by the broad and probably mature valley of the Pecos River. On the east, it is strongly undercut by the retrogressive erosion of the headwaters of the Red, Brazos, and Colorado rivers of Texas and presents a ragged escarpment approximately 500 to 800 ft high, overlooking the central denuded area of that state. There, between the Brazos and Colorado rivers, occurs a series of isolated outliers capped by limestone that underlies both the Llano Uplift on the west and the Grand Prairies escarpment on the east. The southern and narrow part of the table-land, called the Edwards Plateau, is more dissected than the rest, and falls off to the south in a frayed-out fault scarp. This scarp overlooks the coastal plain of the Rio Grande embayment. The central denuded area, east of the Llano, resembles the east-central section of the plains in exposing older rocks. Between these two similar areas, in the space limited by the Canadian and Red Rivers, rise the subdued forms of the Wichita Mountains in Oklahoma, the westernmost member of the Ouachita system.

Other terminology
The term "Western Plains" is used to describe the ecoregion of the Great Plains, or alternatively the western portion of the Great Plains.

Climate
In general, the Great Plains have a wide range of weather, with very cold and harsh winters and very hot and humid summers. Wind speeds are often very high, especially in winter.

The 100th meridian roughly corresponds with the line that divides the Great Plains into an area that receives 20 in or more of rainfall per year and an area that receives less than 20 in. In this context, the High Plains, as well as Southern Alberta, south-western Saskatchewan and Eastern Montana are mainly semi arid steppe land and are generally characterised by rangeland or marginal farmland. The region (especially the High Plains) is periodically subjected to extended periods of drought; high winds in the region may then generate devastating dust storms. The eastern Great Plains near the eastern boundary falls in the humid subtropical climate zone in the southern areas, and the northern and central areas fall in the humid continental climate.

Many thunderstorms occur in the plains in the spring through summer. The southeastern portion of the Great Plains is the most tornado active area in the world and is sometimes referred to as Tornado Alley.

Flora
The Great Plains are part of the floristic North American Prairies Province, which extends from the Rocky Mountains to the Appalachians.

Mammals
Although the American bison (Bison bison) historically ranged throughout much of North America (from New York to Oregon and Canada to northern Mexico), they are strongly associated with the Great Plains where they once roamed in immense herds. Pronghorn (Antilocapra americana) range into western areas of the region. The black-tailed prairie dog (Cynomys ludovicianus) is another iconic species among several rodents that are linked to the region including the thirteen-lined ground squirrel (Ictidomys tridecemlineatus), spotted ground squirrel (Xerospermophilus spilosoma), Franklin's ground squirrel (Poliocitellus franklinii), plains pocket gopher (Geomys bursarius), hispid pocket mouse (Chaetodipus hispidus), olive-backed pocket mouse (Perognathus fasciatus), plains pocket mouse (Perognathus flavescens), and plains harvest mouse (Reithrodontomys montanus), Two carnivores associated with the Great Plains include the swift fox (Vulpes velox) and the endangered black-footed ferret (Mustela nigripes).

Birds
The lesser prairie chicken (Tympanuchus pallidicinctus) is endemic to the Great Plains and the distribution of the greater prairie chicken (Tympanuchus cupido) predominantly occurs in the region, although the latter historically ranged further eastward. The Harris's sparrow (Zonotrichia querula) spends winter months in southern areas of the region. Other species migrate from the south in the spring and spend their breeding season on the plains, including the white-faced ibis (Plegadis chihi), mountain plover (Charadrius montanus), marbled godwit (Limosa fedoa), Sprague's pipit (Anthus spragueii), Cassin's sparrow (Peucaea cassinii), Baird's sparrow (Centronyx bairdii), lark bunting (Calamospiza melanocorys), chestnut-collared longspur (Calcarius ornatus), thick-billed longspur or McCown's longspur (Rhynchophanes mccownii), and dickcissel (Spiza americana).

Reptiles
The prairie rattlesnake (Crotalus viridis) ranges throughout much of the Great Plains and into the valleys and lower elevations of the eastern Rocky Mountains and portions of the American southwest. Other snakes include the plains hog-nosed snake (Heterodon nasicus), western milksnake (Lampropeltis gentilis), great plains ratsnake (Pantherophis emoryi), bullsnake (Pituophis catenifer sayi), plains black-headed snake (Tantilla nigriceps), plains gartersnake (Thamnophis radix), and lined snake (Tropidoclonion lineatum). Reptile diversity increases significantly in southern regions of the Great Plains. The ornate box turtle (Terrapene ornata) and great plains skink (Plestiodon obsoletus) occur in southern areas.

Amphibians
Although few salamanders are strongly associated with region, the western tiger salamander (Ambystoma mavortium) ranges through much of the Great Plains and the Rocky Mountains, as does the Rocky Mountain toad (Anaxyrus w. woodhousi). Other anurans related to region include the Great Plains toad (Anaxyrus cognatus), plains leopard frog (Lithobates blairi), and plains spadefoot toad (Spea bombifrons).

Fish
Some species predominately associated with various river basins in the Great Plains include sturgeon chub (Macrhybopsis gelida), peppered chub (Macrhybopsis tetranema), prairie chub (Macrhybopsis australis), western silvery minnow (Hybognathus argyritis), plains minnow (Hybognathus placitus), smalleye shiner (Notropis buccula), Arkansas River shiner (Notropis girardi), Red River shiner (Notropis bairdi), Topeka shiner (Notropis topeka), plains topminnow (Fundulus sciadicus), plains killifish (Fundulus zebrinus), Red River pupfish (Cyprinodon rubrofluviatilis), and Arkansas darter (Etheostoma cragini).

Invertebrates
The great plains also has many invertebrate species living here both alive and extinct such as the American burying beetle (Nicrophorus americus), Salt Creek Tiger Beetle (Cinidela nevadica lincolniana), Great Plains Giant Tiger Beetle (Amblycheila chylindriformis),, Microstylum morosum, Bean leaf beetle (Cerotoma trifurcata), Great Plains Camel Cricket (Daihinia brevipes), and the Great plains spittlebug (Lepyronia gibbosa). Some species in the Great plains have gone extinct in the great plains like the Rocky Mountain Locust (Melanoplus spretus).

Paleontology
During the Cretaceous Period (145–66 million years ago), the Great Plains were covered by a shallow inland sea called the Western Interior Seaway. However, during the Late Cretaceous to the Paleocene (65–55 million years ago), the seaway had begun to recede, leaving behind thick marine deposits and a relatively flat terrain which the seaway had once occupied.

During the Cenozoic era, specifically about 25 million years ago during the Miocene and Pliocene epochs, the continental climate became favorable to the evolution of grasslands. Existing forest biomes declined and grasslands became much more widespread. The grasslands provided a new niche for mammals, including many ungulates and glires, that switched from browsing diets to grazing diets. Traditionally, the spread of grasslands and the development of grazers have been strongly linked. However, an examination of mammalian teeth suggests that it is the open, gritty habitat and not the grass itself which is linked to diet changes in mammals, giving rise to the "grit, not grass" hypothesis.

Paleontological finds in the area have yielded bones of mammoths, saber-toothed cats and other ancient animals, as well as dozens of other megafauna (large animals over 100 lb) – such as giant sloths, horses, mastodons, and American lion – that dominated the area of the ancient Great Plains for thousands to millions of years. The vast majority of these animals became extinct in North America at the end of the Pleistocene (around 13,000 years ago).

A number of significant fossil sites are located in the Great Plains including Agate Fossil Beds National Monument (Nebraska), Ashfall Fossil Beds (Nebraska), Clayton Lake State Park (New Mexico), Dinosaur Valley State Park (Texas), Hudson-Meng Bison Kill (Nebraska), Makoshika State Park (Montana), and The Mammoth Site (South Dakota).

Public and protected lands
Public and protected lands in the Great Plains include National Parks and National Monuments, administers by the National Park Service with the responsibility of preserving ecological and historical places and making them available to the public. The U.S. Fish & Wildlife Service manages the National Wildlife Refuges, with the primary responsibility of conserving and protecting fish, wildlife, plants, and habitat in the public trust. Both are agencies of the Department of the Interior.

In contrast, U.S. Forest Service, an agency of the U. S. Department of Agriculture, administers the National Forests and National Grasslands, under a multiple-use concept. By law, the U.S. Forest Service must consider all resources, with no single resource emphasized to the detriment of others, including water, soil, grazing, timber harvesting, and minerals (mining and drilling), as well as recreation and conservation of fish and wildlife. Each individual state also administers state lands, typically smaller areas, for various purposes including conservation and recreation.

Grasslands are among the least protected biomes. Humans have converted much of the prairies for agricultural purposes or to create pastures. Several of the protected lands in the region are centered around aberrant and uncharacteristic features of the region, such as mountains, outcrops, and canyons (e.g. Devil's Tower National Monument, Wind Cave National Park, Scotts Bluff National Monument), and as splendid and worthy as they are, they are not primarily focused on conserving the plains and prairies.

 * Alberta: Elk Island National Park (48,000 acre), Suffield National Wildlife Area (113,263 acre).
 * Colorado: Comanche National Grassland (443,081 acre), Pawnee National Grassland (193,060 acre).
 * Iowa: DeSoto National Wildlife Refuge (8,362 acre)
 * Kansas: Cheyenne Bottoms Wildlife Area (41,000 acre), Cimarron National Grassland (108,176 acre), Flint Hills National Wildlife Refuge (18,463 acre), Kirwin National Wildlife Refuge (10,778 acre), Marais des Cygnes National Wildlife Refuge (7,500 acre), Quivira National Wildlife Refuge (22,135 acre), Tallgrass Prairie National Preserve (10,882 acre).
 * Manitoba: Riding Mountain National Park (733,400 acre), Turtle Mountain Provincial Park (46,080 acre).
 * Oklahoma: Black Kettle National Grassland (31,286 acre), Salt Plains National Wildlife Refuge (32,080 acre), Wichita Mountains Wildlife Refuge (59,000 acre).
 * Missouri: Loess Bluffs National Wildlife Refuge (7,350 acre).
 * Minnesota: Agassiz National Wildlife Refuge (61,500 acre), Big Stone National Wildlife Refuge (11,586 acre), Glacial Lakes State Park (2,423 acre), Blue Mounds State Park (1,567 acre).
 * Montana: Charles M. Russell National Wildlife Refuge (915,814 acre), Makoshika State Park (11,538 acre), Medicine Lake National Wildlife Refuge (31,533 acre), Rosebud Battlefield State Park (3,052 acre), UL Bend National Wildlife Refuge (56,048 acre), Upper Missouri River Breaks National Monument (377,000 acre).
 * Nebraska: Scotts Bluff National Monument (3,000 acre), Boyer Chute National Wildlife Refuge (4,040 acre), Crescent Lake National Wildlife Refuge (45,818 acre), Fort Niobrara National Wildlife Refuge (19,131 acre), John and Louise Seier National Wildlife Refuge (2,400 acre), North Platte National Wildlife Refuge (5,047 acre), Rainwater Basin Wetland Management District (22,864 acre), Valentine National Wildlife Refuge (71,516 acre).
 * New Mexico: Grulla National Wildlife Refuge (3,236 acre), Kiowa National Grassland (137,131 acre).
 * North Dakota: Arrowwood National Wildlife Refuge (15,934 acre), Audubon National Wildlife Refuge (14,739 acre), Little Missouri State Park (6,492 acre), Sheyenne National Grassland (70,180 acre), Theodore Roosevelt National Park (70,446 acre).
 * Saskatchewan: Grasslands National Park (224,000 acre), Last Mountain Lake National Wildlife Area (38,553 acre).
 * South Dakota: Badlands National Park (242,756 acre), Black Hills National Forest (1,253,308 acre), Custer State Park (71,000 acre), Fort Pierre National Grassland (115,890 acre), Grand River National Grassland (154,783 acre), Wind Cave National Park (33,847 acre).
 * Texas: Buffalo Lake National Wildlife Refuge (7,664 acre), Caddo National Grassland (17,873 acre), Caprock Canyons State Park (15,313 acre), Hagerman National Wildlife Refuge (11,320 acre), Lyndon B. Johnson National Grassland (20,309 acre), Muleshoe National Wildlife Refuge (6,440 acre), Palo Duro Canyon State Park (26,200 acre), Rita Blanca National Grassland (230,000 acre).
 * Wyoming: Curt Gowdy State Park (3,395 acre), Devil's Tower National Monument (1,346 acre), Glendo State Park (ca. 10,000 acre of land), Thunder Basin National Grassland (547,499 acre).

Ecological changes
the Great Plains biome is found to be at the brink of collapse due to woody plant encroachment, with 62% of Northern American grassland lost to date.

Original American contact
The first Peoples (Paleo-Indians) arrived on the Great Plains thousands of years ago. The introduction of corn around 800 CE allowed the development of the mound-building Mississippian culture along rivers that crossed the Great Plains and that included trade networks west to the Rocky Mountains. Mississippians settled the Great Plains at sites now in Oklahoma and South Dakota.

Siouan language speakers may have originated in the lower Mississippi River region. They were agriculturalists and may have been part of the Mound Builder civilization during the 9th–12th centuries.

Pressure from other Indian tribes, themselves driven west and south by the encroachment of European settlers as well as economic incentives such as the fur trade, alongside the arrival of the horse and firearms from Europe pushed multiple tribes onto the Great Plains.

Among those to have lived on the Great Plains were the Blackfoot, Crow, Sioux, Cheyenne, Arapaho, Comanche, and others. Eastern portions of the Great Plains were inhabited by tribes who lived at Etzanoa and in semi-permanent villages of earth lodges, such as the Arikara, Mandan, Pawnee, and Wichita.

Wars with the Ojibwe and Cree peoples pushed the Lakota (Teton Sioux) west onto the Great Plains in the mid- to late-17th century. The Shoshone originated in the western Great Basin and spread north and east into present-day Idaho and Wyoming. By 1500, some Eastern Shoshone had crossed the Rocky Mountains into the Great Plains. After 1750, warfare and pressure from the Blackfoot, Crow, Lakota, Cheyenne, and Arapaho pushed Eastern Shoshone south and westward. Some of them moved as far south as Texas, emerging as the Comanche by 1700.

Arrival of horses
The first known contact between Europeans and Indians in the Great Plains occurred in what is now Texas, Kansas, and Nebraska from 1540 to 1542 with the arrival of Francisco Vázquez de Coronado, a Spanish conquistador. In that same period, Hernando de Soto crossed a west-northwest direction in what is now Oklahoma and Texas which is now known as the De Soto Trail. The Spanish thought that the Great Plains were the location of the mythological Quivira and Cíbola, a place said to be rich in gold.

People in the southwest began to acquire horses in the 16th century by trading or stealing them from Spanish colonists in New Mexico. As horse culture moved northward, the Comanche were among the first to commit to a fully mounted nomadic lifestyle. This occurred by the 1730s, when they had acquired enough horses to put all their people on horseback.

The real beginning of the horse culture of the plains began with the Pueblo Revolt of 1680 in New Mexico and the capture of thousands of horses and other livestock. In 1683 a Spanish expedition into Texas found horses among Native people. In 1690, a few horses were found by the Spanish among the Indians living at the mouth of the Colorado River of Texas and the Caddo of eastern Texas had a sizeable number.

The French explorer Claude Charles Du Tisne found 300 horses among the Wichita on the Verdigris River in 1719, but they were still not plentiful. Another Frenchman, Bourgmont, could only buy seven at a high price from the Kaw in 1724, indicating that horses were still scarce among tribes in Kansas. By 1770, that Plains Indians culture was mature, consisting of mounted buffalo-hunting nomads from Saskatchewan and Alberta southward nearly to the Rio Grande.

The milder winters of the southern Plains favored a pastoral economy by the Indians. On the northeastern Plains of Canada, the Indians were less favored, with families owning fewer horses, remaining more dependent upon dogs for transporting goods, and hunting bison on foot. The scarcity of horses in the north encouraged raiding and warfare in competition for the relatively small number of horses that survived the severe winters.

Comanche power peaked in the 1840s when they conducted large-scale raids hundreds of miles into Mexico proper, while also warring against the Anglo-Americans and Tejanos who had settled in independent Texas.

Fur trade
The fur trade brought thousands of colonial settlers into the Great Plains over the next 100 years. Fur trappers made their way across much of the region, making regular contacts with Indians.

The Hudson's Bay Company (HBC) had first been granted in 1670 a commercial monopoly over the huge Hudson Bay drainage area known as Rupert's Land covering a northern portion of the Great Plains. The North West Company fur trade incumbent had also been present in the area until acquired by the HBC during the early 1820s.

The United States acquired the Louisiana Purchase in 1803 and conducted the Lewis and Clark Expedition in 1804–1806, and more information became available concerning the Plains, and various pioneers entered the areas. Fur trading posts were often the basis of later settlements. Through the 19th century, more settlers migrated to the Great Plains as part of a vast westward expansion of population, and new settlements became dotted across the Great Plains.

The settlers also brought diseases against which the Indians had no resistance. Between a half and two-thirds of the Plains Indians are thought to have died of smallpox by the time of the Louisiana Purchase. The 1837 Great Plains smallpox epidemic spread across the Great Plains, killing many thousands between 1837 and 1840. In the end, it is estimated that two-thirds of the Blackfoot population died, along with half of the Assiniboines and Arikaras, a third of the Crows, and a quarter of the Pawnees.

Settlement
Beginning in 1821, the Santa Fe Trail ran from the Missouri River to New Mexico, skirting north of Comancheria. Beginning in the 1830s, the Oregon Trail led from the Missouri River across the Great Plains.

Much of the Great Plains became open range where cattle roamed free, hosting ranching operations where anyone was free to run cattle. In the spring and fall, ranchers held roundups where their cowboys branded new calves, treated animals, and sorted the cattle for sale. Such ranching began in Texas and gradually moved northward. Between 1866 and 1895, cowboys herded 10 million cattle north to rail heads such as Dodge City, Kansas and Ogallala, Nebraska; from there, cattle were shipped east.

Passage of the Kansas-Nebraska Act in 1854 opened both territories to White settlement. The Homestead Acts of 1862 further encouraged settlement and agricultural development in the Great Plains; the population of Nebraska, for instance, increased from under 30,000 in 1860 to over one million in 1890. A homesteader was permitted to claim up to 160 acre of land for only a small filing fee, provided that he or she lived on the land for a period of five years and cultivated it. The provisions were expanded under the Kinkaid Act of 1904 to include a homestead of an entire section. Hundreds of thousands of people claimed such homesteads, sometimes building houses out of the very turf of the land. Many of them were not skilled farmers, and failures were frequent. The Canadian Dominion Lands Act of 1871 served a similar function for establishing homesteads on the prairies in Canada.

Railroads
After 1870, the new railroads across the Plains brought hunters who killed off almost all the bison for their hides. The railroads offered attractive packages of land and transportation to American farmers, who rushed to settle the land. They also took advantage of the homestead laws to obtain farms. Land speculators and local boosters identified many potential towns, and those reached by the railroad had a chance, while the others became ghost towns. Towns flourished if they were favored by proximity to the railroad.

The population of Minnesota, Dakota, Nebraska, and Kansas experienced significant growth during the 1870s. The total population in these states grew from 1.0 million in 1870 to 2.4 million in 1880, more than doubling in just 10 years. The number of farms in the region tripled, increasing from 99,000 in 1870 to 302,000 in 1880. The improved acreage (land under cultivation) quintupled, rising from 5.0 million acres to 24.6 million acres during the same period. the new settlers mostly purchased land on generous terms from transcontinental railroads that were given land grants by Washington. They focused on wheat and cattle. This rapid population influx and agricultural expansion was a hallmark of the settlement and development of the Great Plains in the late 19th century, as the region attracted waves of new settlers from Germany, Scandinavia, and Russia, as well as farmers who sold land in older states to move to larger farms.

First settlements
The first White settlements in the great plains were forts, particularly along the Santa Fe Trail, and trading posts. Some of the first built were:
 * Fort Lisa (1809), North Dakota
 * Red River Colony or Selkirk Settlement (1811), Manitoba
 * Fort Lisa (1812), Nebraska
 * Fort Atkinson (Nebraska) (1819), Nebraska
 * Fontenelle's Post (1822), Nebraska
 * Cabanne's Trading Post (1822), Nebraska
 * Fort Kiowa (1822), South Dakota
 * Fort Laramie (1834), Texas
 * Fort Parker (1834), Texas
 * Zinkenburg (1845), Texas
 * Fort Kearney (1848), Nebraska
 * Fort Martin Scott (1848), Texas
 * Fort Croghan (1849), Texas
 * Fort Gates (1849), Texas
 * Fort Graham (1849), Texas
 * Fort Worth (1849), Texas
 * Fort Belknap (1851), Texas
 * Fort Mason (1851), Texas
 * Fort Chadbourne (1852), Texas
 * Fort McKavett (1852), Texas
 * Fort Phantom Hill (1852), Texas
 * Camp Colorado (1855), Texas
 * Fort McPherson (1863), Nebraska
 * Fort Mitchell (1864), Nebraska
 * Fort Concho (1867), Texas
 * Fort Griffin (1867), Texas
 * Fort Richardson (1867), Texas
 * Fort Sidney (1867), Nebraska
 * Fort Omaha (1868), Nebraska
 * Fort Hartsuff (1874), Nebraska
 * Fort Sill (1869), Oklahoma
 * Fort Robinson (1874), Nebraska
 * Camp Sheridan (1874), Nebraska
 * Fort Niobrara (1880), Nebraska
 * Fort Elliott (1875), Texas

Social life

The railroads opened up the Great Plains for settlement, making it possible to ship wheat and other crops at low cost to the urban markets in the East and overseas. Homestead land was free for American settlers. Railroads sold their land at cheap rates to immigrants in the expectation that they would generate traffic as soon as farms were established. Immigrants poured in, especially from Germany and Scandinavia. On the plains, very few single men attempted to operate a farm or ranch by themselves; they understood the need for a hard-working wife and numerous children to handle the many responsibilities. During the early years of settlement, farm women played an integral role in assuring family survival by working outdoors. After approximately one generation, women increasingly left the fields, thus redefining their roles within the family. New technology encouraged women to turn to domestic roles, including sewing and washing machines. Media and government extension agents promoted the "scientific housekeeping" movement, along with county fairs which featured achievements in home cookery and canning, advice columns for women regarding farm book keeping, and home economics courses in the schools.

The eastern image of farm life in the prairies emphasized the isolation of the lonely farmer and wife, yet plains residents created busy social lives for themselves. They often sponsored activities which combined work, food, and entertainment, such as barn raisings, corn huskings, quilting bees, Grange meetings, church activities and school functions. Women organized shared meals and potluck events, as well as extended visits among families.

Progressive Era
The Progressive movement was a reform movement that took place in all parts of the country during the late 19th and early 20th centuries. The movement sought to address social, political, and economic problems that had arisen as a result of the Industrial Revolution. Progressives believed that the government could play a role in solving these problems by regulating businesses, protecting workers, and providing social welfare programs.

The Plains states were a hotbed of Progressive activity. Many of the reforms that were enacted at the national level were first implemented in the Plains states. For example, the initiative and referendum process, which allows voters to directly enact laws, was first adopted in South Dakota in 1898. The direct primary, which allows voters to choose their party's candidates in primary elections, was first adopted in Wisconsin in 1903.

Progressive reformers in the Great Plains focused on high priority issues, especially:
 * Regulation of railroads and public utilities
 * Prohibition
 * Employer liability and workers' compensation
 * Protections for consumers
 * State-owned enterprises
 * Woman suffrage

Progressives in the Great Plains were more likely to support direct democracy, woman suffrage, and Prohibition than their counterparts elsewhere. They were also more likely to favor state-owned enterprises, especially those devoted to economic development. Plains progressivism was more radical than progressivism in eastern states, with a greater focus on direct democracy, woman suffrage, and Prohibition. Plains progressives were more isolationist regarding foreign policy, largely in response to the large German and Scandinavian elements. Socialists were more active than elsewhere, Progressive reforms had a significant long-term impact on the region. They helped to improve the lives of workers, farmers, and consumers. They also helped to make the Plains states more democratic and responsive to the needs of their citizens.

Dust Bowl and water resources
The region roughly centered on the Oklahoma Panhandle was known as the Dust Bowl during the late 1920s and early 1930s, including southeastern Colorado, southwestern Kansas, the Texas Panhandle, and extreme northeastern New Mexico. The effects of an extended drought, inappropriate cultivation, and financial crises of the Great Depression forced many farmers off the land throughout the Great Plains.

From the 1950s on, many areas of the Great Plains have become productive crop-growing areas because of extensive irrigation on large land-holdings. The United States is a major exporter of agricultural products. The southern portion of the Great Plains lies over the Ogallala Aquifer, a huge underground layer of water-bearing strata. Center pivot irrigation is used extensively in drier sections of the Great Plains, resulting in aquifer depletion at a rate that is greater than the ground's ability to recharge.

Population decline
The rural Plains have lost a third of their population since 1920. Several hundred thousand square miles of the Great Plains have fewer than 6 PD/sqmi, the density standard that Frederick Jackson Turner used to declare the American frontier "closed" in 1893. Many have fewer than 2 PD/sqmi. There are more than 6,000 ghost towns in Kansas alone, according to Kansas historian Daniel Fitzgerald. This problem is often exacerbated by the consolidation of farms and the difficulty of attracting modern industry to the region. In addition, the smaller school-age population has forced the consolidation of school districts and the closure of high schools in some communities. The continuing population loss has led some to suggest that the current use of the drier parts of the Great Plains is not sustainable, and there has been a proposal to return approximately 139000 sqmi of these drier parts to native prairie land as a Buffalo Commons.

Wind power
The Great Plains contributes substantially to wind power in the United States. T. Boone Pickens developed wind farms after a career as a petroleum executive, and he called for the U.S. to invest $1 trillion to build an additional 200,000 MW of wind power in the Plains as part of his Pickens Plan. He cited Sweetwater, Texas, as an example of economic revitalization driven by wind power development.

International steppe-lands

 * Eurasian Steppe
 * Kazakh Steppe
 * Pampas, in Argentina, Uruguay, Brazil
 * Pontic–Caspian steppe
 * Puszta

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Great Plains