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3 00215~ THE REG ION The Lower Colorado Region includes the Colorado River drainage in the United States below Lee Ferry, Arizona, except that occurring in California (see map). In addition, it includes several closed basins in Arizona, Nevada, and New Mexico, and some areas in southern Arizona and New Mexico that drain into Mexico. The Region occupies 141,137 square miles in the Pacific Southwest area of the United States. Of this total area, 106,982 sqQare miles are in Arizona, 17,310 square miles are in Nevada, 13,355 sqQare miles are in New Mexico, and 3,490 square miles are in Utah. The population is concentrated principally in south central Arizona and southern Nevada. The remainder of the Region's population is located in small, widely scattered communities. Much of the area is uninhabited. The Lower Colorado Region is composed of a complex of plateaus, mOQntains, deserts, and plains, with elevations ranging from 75 feet above sea level, near Yuma, Arizona, to more than 12,600 feet at Humphreys Peak, near Flagstaff, Arizona. The climate of the Region varies as widely as does its topography. Maximum temperatQres range from more than 100 degrees in the desert to the mild 70' s in the mO\mtainoQs areas. Average annual precipitation varies from less than 5 inches at Yuma to more than 30 inches in the higher mountains. The Lower Colorado ;~eGion has a wide variation in vegetal cover types. The forest types extend from the small alpine areas on top of Ghe hiGhest mOQntain peaks; through the coniferoQs forest zones of sprQce-fir, Ponderosa pine, and the pinon-juniper and oak woodlands, and the chaparral types. The rangeland type extends from the forest type through the northern and southern desert shrQbs, the northern and desert grasslands, do~m throQgh a small area of true desert near the mouth of the Colorado River on the bOQndary between Mexico and Arizona. Scattered throughoQt the Region are areas of cultivated land, including irrigated pastQre, with the largest blocks in the lower Gila and the southern half of the Lower Main stem Subregions. More than 500,000 acres of the Rp.gion are developed as Qrban and industrial areas. More than 340,000 a':res of the Region are occupied by water in the form of streams, lakes, and reservoirs. About 52 percent of the total land is federally owned, 12 percent is in state and other public ownership, and 36 percent i" private land. About one-half of the latter is in Indian reservations held in trust by the Federal government.