Geography of The Interior United States - The Great Plains

The Great Plains

A broad stretch of country underlain by nearly horizontal strata extends westward from the 97th meridian west to the base of the Rocky Mountains, a distance of from 300 to 500 miles (480 to 800 km). It extends northward from the Mexican boundary far into Canada. This is the province of the Great Plains. Although the altitude of the plains increases gradually from 600 or 1,200 ft (370 m) on the east to 4,000-5,000 or 6,000 feet (1,800 m) near the mountains, the local relief is generally small. The sub-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 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. The plains may be described in northern, intermediate, central and southern sections, in relation to certain peculiar features.