OCR Text |
Show across the Colorado River Basin from the southern boundary of Utah through Arizona to western New Mexico. This barrier is formed by the Grand Wash Cliffs, the Coconino and Kaibab Plateaus, the San Francisco group of volcanic peaks which rise above 12,000 feet, the long but narrow Mogollon Plateau averaging above 7,000 feet, and the 11,000- foot crests of the White Mountains. Heavy snowfall, long winters, and cool summers with afternoon thunderstorms characterize the climate of most of these highlands. West and south of this last barrier lies the great southern desert of Nevada, Arizona, California, and Mexico. Rainfall is scanty and the summer season long and intensely hot. Winters are mild. Many low mountains rise from this desert. The most important of these ranges are the Hualpai, Harquahala, Santa Maria, Bradshaw, Pinal, Santa Catalina, Rin- con, Galiuro, Pinaleno, Santa Rita, and Chiricahua Mountains. They comprise a series of cool islands rising out of the surrounding desert heat rather than a climatic or physiographic barrier. The life zone map ( PI. 12, in pocket) summarizes graphically the natural features of the Colorado River Basin. It indicates the climates of the basin and their characteristic plants and animals. In view of the close relation between temperatures and altitudes, to be described later, the map also shows enough of the topography to furnish a rough three- dimensional presentation of the basin, the extent of the many great plateaus, the island- like distribution of many of the southern mountain ranges, and the deep penetration of the Rocky Mountains by numerous long, winding valleys. The life zone map indicates the nature and distribution of the basin's various recreational regions. The Lower Sonoran Zone is principally a winter recreation region, where the desert scenery and sunshine are ideal for photography, swimming, camping, hiking, horseback riding, and motoring, and where some hunting and fishing may be enjoyed. The Upper Sonoran Zone, in valley and plains lands, provides recreational opportunities similar to those of the Lower Sonoran Zone, but is usable in summer when the latter region is too hot for comfort. The northern limit of the Upper Sonoran Zone is generally open sagebrush country not suitable for winter recreation. Figure 5.- The great southern desert- Organ Pipe Cactus National Monument, Ariz. |