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