340 THE COLORADO DESERT 



co\\Vi<e of less than six montlis," saj's Bandolier, '" the Spanish recon- 

 noitering coi'i)S had thus three times touched the largest river of 

 western America, had explored its shores witli toleral)le accuracy for 

 a considerahle length of its course, and had also traveled in two direc- 

 tions through i)arts of Arizona which have only in verv recent time 

 again attracted attention." 



The arid region .of North America covers a large area. Through- 

 out there is presented that strange uniformity of ])h_ysical features 

 and life-forms that characterizes deserts the world over. The southern 

 ])ortion of the Colorado Desert possesses, however, bizarre and curious 

 features of its own. Its area is commonly understood to comprise 

 the great depressed valley lying half in southern California and half 

 in Lower California, inclosed on the west by the southward exten- 

 sions of the San Jacinto Mountains, on the north b}- the desert range 

 of the San Bernardino and Chocolate Mountains in California, and 

 on the south by the course of the Colorado River fiom .Arizona to 

 the gulf. 



In ver}^ recent geological times this region was an arm of the sea 

 and the Colorado River reached the Pacific Ocean at Yuma. 'J'he 

 geological changes that won this valle}' from the gulf seem to have 

 been two: tlie upbuilding of an enormous delta iVi^m the deposits of 

 the Colorado, and the crustal elevation of the eartli l)eneath the cen- 

 tral region covered by this delta to a height sufficient to divide the 

 depression and to retire the gulf to its present shores far south of the 

 line, wliile it left the U[)per part still below tiie level of the sea.* These 

 movements tunned the Colorado River into the region still depressed 

 and transformed it into a splendid fresh-water lake. The evidence 

 of the extent of this bod}^ of fresh water is most interesting. Its old 

 floor remains, a deep accumulation of fine, tluviatile soil, rich as the 

 delta of Eg3^])t, which in ])laces is whitened l»y myriads of fresh-water 

 shells, several small univalves, and a single bivalve, vai'ieties of am- 

 nicola and anadrovi siUl to be found alive in tlie Colorado itself. For 

 miles along the mountain bases at the northern end, where the still 

 waters of the lake once reached, there runs a broad, white band of cal- 

 careous deposit from the tiny mollusca that at one time inhabited its 

 shores. Graduall}', however, the river wliicli fed this lake by its con- 

 stant deposits built up an elevated flood-plain about its mouth that 

 diverted its waters more and more away from the lake until the main 

 channel, imjiounded in levees of its own making, carried the current 



♦Salton, the lowfst |fiiint in the desert, is given ;it ii'.:'. fret lielc.w se;i-level, uiiile Vuiiiti is 

 275 feet above. 



