Defining the Great Plains

Borders of the Great Plains

The Great Plains region is the vast natural grassland that stretches across central North America from the Rocky Mountains to the woodlands of the Midwest.

We define the limits of the Great Plains as follows:

North: The Canadian border
South: The 32nd parallel
West: 5,000 feet of elevation
East: The line of 700 mm of average annual precipitation

All regionalization is necessarily somewhat arbitrary, and we do not claim a monopoly on the definition of the Great Plains. In fact, precise borders elude consensus and each of our boundary lines is open to debate:

North/South: Arguably, the Great Plains extend north into Canada and south through Texas to Mexico. We have chosen northern and southern borders that maximize data uniformity and comparability.
West: The Rocky Mountains are commonly agreed to bound the Great Plains on the west, but exactly where in the Rockies to draw this line remains in dispute.
East: The only agreement on this boundary is that no authoritative line exists. Numerous people have attempted to define this border in both physiographical and cultural terms, using such demarcators as:

Our boundaries depend on a combination of climatic, topographical, political, and cartographic criteria, and are ultimately drawn along county borders. According to these definitions, the Great Plains region contains about 475 counties in twelve states.

Great Plains and Surrounding Counties in 2000

Characteristics of the Great Plains

As we have defined them, the counties belonging to the Great Plains share some environmental characteristics, but also differ from one another in terms of soil composition, temperature, precipitation, and elevation. The Great Plains region is just as hard to classify as it is to delineate, and can be subdivided according to a number of criteria:

East/West: Rainfall in the plains decreases from east to west. As a result, the eastern plains are quite arable, while the western plains are more suited to pastoral purposes. Natural vegetation in the east is dominated by tallgrass prairie and in the west by shortgrass steppe.

North/South: Average temperatures in the Great Plains increase from north to south, with mean annual temperatures ranging from less than 0°C to greater than 20°C.

High/Low: High plain rises more than 2,000 feet above sea level and slopes ever upward as it moves west.

This environmental diversity is mirrored in the diversity of attitudes toward the Great Plains, which have been romanticized as a fertile land of possibility and reviled as the Great American Desert. Therefore, the Great Plains both attract and repel population. The region thus includes major cities, areas with population densities of fewer than two people per square mile, and several gradations in between.

Across this diversity, however, the Great Plains counties are united by the flat or slightly rising treeless expanse that must have greeted all early visitors, extreme climates and dramatic weather patterns, and a preponderance of grasses in the natural vegetation.