EXTINCT FAUNAS OF THE MOHAVE DESERT 249 



area are sharply marked by the abruptly rising wall of the bordering 

 mountain ranges. The limits to the east are not so clearly marked, 

 being considered by some to reach the eastern border of the state; by 

 others they are held to extend less than half the distance to the Colorado 

 Eiver. 



The elevation of the desert floor ranges from 2,000 ft. approximately 

 to 4,000 ft. above the sea, in sharp contrast to the basin of the Salton 

 Sea, which extends below the level of the ocean a short distance to the 

 south. The topography of the region is characterized by great stretches 

 of open plains many miles in extent, over which scattered mountain 

 peaks or ranges are distributed with little suggestion of order in their 

 arrangement. 



The total rainfall of the desert amounts only to a few inches per 

 year. Living streams are rare, and travel in all of this region is neces- 

 sarily limited by accessibility of the few localities at which potable 

 water can be obtained. Eain falls largely in the middle of the winter 

 season, and throughout the greater part of the year there is no precipi- 

 tation. The water at times comes with a rush, flows off rapidly as 

 floods, and sometimes causes considerable damage to artificial obstacles 

 in the path of the current. With the exception of the Mohave Eiver, 

 which runs a thin superficial stream for a considerable portion of the 

 year, there are very few points at which a supply of water can be ob- 

 tained on the surface. Investigation has shown that artesian water is 

 available over certain areas, and agriculturists have operated to some 

 extent by irrigation with water obtained from wells. 



The diminished rainfall, the unhindered influence of a brilliant sun 

 and the moderate altitude have given to the Mohave a distinctly arid 

 climate; and with the climate go all of the accompanying character- 

 istics of life, of erosion and deposition, and of the peculiar land forms 

 of an arid country. 



The vegetation of the Mohave area is at the present time limited 

 mainly to desert types, the contrast with the flora beyond the ridge 

 immediately to the west^ being very marked. In crossing the Tehachapi 

 Eange from the Great Valley of California to the Mohave one finds the 

 valleys of the western side thickly studded with oak, sycamore, and 

 willow, and the hills are carpeted with gTass. On the eastern slope the 

 whole aspect of the vegetation changes suddenly, as if one were entering 

 a foreign land. The yuccas and the creosote bush replace oak and 

 grass, and the oddly outstretched arms of the Joshua trees seem every- 

 where raised up as if to attract attention. Plants of arboreal type are 

 rare, and, excepting a few junipers, the j^uccas furnish the only trees. 

 Creosote bushes are generally present, but are sometimes sparingly rep- 

 resented. Perhaps to show that under adverse conditions nature means 

 only to be just and not unkind, the spring and early summer find the 



