72 PROCEEDINGS OF THE ACADEMY OF [VOL. LXXIV 



include the bordering detrital slopes from the contiguous mountains. 

 So restricted, the area is practically coterminous with the ancient 

 beach-lines and terraces of the lakes whic hoccupied the valley." 



"Its area is estimated at not less than 2,100 square miles, its 

 breadth east and west opposite Carrizo Creek about 33 miles. Its 

 height above tide ranges from 135 feet above sea-level at Yuma to 

 an average of 42 feet following the old shore line of Cahuilla Lake, 

 and to minus 187 feet, now partly submerged." 



The only possible criticism of this definition is that restricted 

 in this way it becomes too purely geological and genetic for con- 

 venient application to a physiographic phenomenon like a desert. 

 ( Vrtainly a broadly conceived faunistic study of the region cannot 

 so confine itself. For the purpose of such a study most workers 

 will find it more practicable to define the region as that roughly 

 enclosed on the north and northeast by the desert slopes of the 

 San Bernardino Mountains and the divide which is formed by 

 their depauperate southeastern spurs, the Cottonwood, Chucka- 

 walla, and Chocolate Mountains, and which separates the Cahuilla 

 Basin from the more diffused Mojave Desert further north; on 

 the east and southeast by the Colorado River; and on the south- 

 west and west by the eastern escarpment of the Peninsular Range 

 and the Santa Rosa and San Jacinto Mountains. The entire area 

 will even then fall within the confines of the single major life zone 

 known as the Lower Sonoran, unless one prefers to draw the desert 

 boundary far enough up the circumventing mountains to include 

 some portions of the Upper Sonoran zone. 



Thus understood the general outline of the desert is roughly tri- 

 angular, with the base on the Colorado River, the apex at the 

 San Gorgonio Pass, and comprising within it the eastern portion 

 of Riverside County, the whole of Imperial County, and a little 

 of the eastern edge of San Diego County, California, while the 

 southern corner of the triangle juts over into the Mexican territory 

 of Lower < alifornia. San Bernardino County is barely touched in 

 the vicinity of the Morongo. If Death Valley be excepted, the 

 region is doubtless quite unique within the borders of the United 

 Slates, if not in the world. From the floor of the Salton Sink which 

 lies 265 feet below sea level, there is a gradual ascent of the desert 

 floor to a line varying from nearly sea-level to about 2,500 feet 

 along i he base of the mountains, which then rise abruptly to vary- 

 ing heights, the most loftly being San Jacinto Peak, with an 

 elevation of 10,805 feel, and San Gorgonio Peak, 11,485 feet high. 

 By reason of their prevailingly granitic formations, lack of foot- 



