TOPOGRAPHIC FEATURES OF THE DESERT BASINS, 45 



THE MOJAVE DRAINAGE SYSTEM. 



The Amargosa was and is essentially a single stream occupying a long, narrow trough. 

 The Quaternary Mojave was more dendritic. Rising in the northern slopes of San 

 Bernardino Peak, it cut, like the Humboldt, directly across the main structural 

 features of the region, entered at Soda Lake a north-south trough which is perhaps 

 related to that of the Amargosa, and followed this north to the junction with the 

 Amargosa and the western turn into Death Valley. How far this course was deter- 

 mined by the structure of the country and how far it was anterior to and imposed 

 upon it, it is impossible to say. The writer is strongly inclined to consider it largely 

 the latter. In any case, from each trough that it cut and each plain that it tapped it 

 received its greater or lesser tributaries each with its own dendritic drainage, or per- 

 haps its chain of lakes. All of this is now changed. Perhaps more than any other 

 American area the Mojave Desert shows the effects of lessened rainfall. It is a country 

 where lakes are dead and streams are dying and where only the occasional arroyos 

 galvanized into vigor by rare and sudden storms maintain the semblance of a drainage. 

 The Mojave River has lost all its tributaries, and its main stream, though fed by the 

 well-watered slopes of San Bernardino Peak, flows no farther than Soda Lake and 

 seldom even so far. Dams of dune sand and alluvium have blocked the greater 

 valleys and cut the flatter areas into a checkerboard of minor basins. ' "Dry lakes" 

 lie in nearly every township. Indeed, so numerous are they that the writer possesses 

 authentic information concerning nearly 50 of them. It would scarcely be profita- 

 ble to review all of these in detail. Larger or smaller, relatively old or relatively 

 young, all were once part of the Mojave and all are post-Lahontan. Rodriguez, 

 Rosamond, Rabbit, and Harper Lakes in the west, and Coyote, Coolgardie, Cronese, 

 Garlic, and Langford Lakes to the north, are among the most important and all are of 

 the same type. 



Some of the larger and older playas are somewhat saline, l^ut tliis salinity is recent 

 and superficial. Even in Soda Lake, which is the present terminus of the Mojave 

 River, waters a score of feet under the surface are practically fresh. North of Soda 

 Lake there is a river channel, but no river. Local rainfall and an occasional brief 

 overflow from Soda Lake have created a small playa at Silver Lake, about 20 miles 

 north. North of this is a dam of recent dune sand and then the valley of the Amargosa 

 and free drainage into Death Valley. 



It has been considered useless to compute the area of the various basins into which 

 the Mojave drainage has been divided. The total is 10,160 square miles. 



THE IVANPAH BASIN. 



The Ivanpah Valley lies'ln the extreme southern end of that offshoot of the Amar- 

 gosa trough which carries the Pahrump Basin (see p. 44). However, the divide which 

 separates it from this trough is high and structural, as are all the other divides which 

 limit the basin. It is practically certain that its inclosed and independent condition 

 is both ancient and permanent. The bottom of the valley now contains two playas 

 of usual character and separated by a very low alluvial divide. There are also in the 

 northeastern end of the basin two small basins and playas, now independent but 

 believed once to have been tributary either by free drainage .or by overflow, probably 

 the latter. The total basin area is 900 square miles. 



THE MESQUITE TROUGH. 



Mention has already been made of the two structural troughs which lie north of 

 and parallel to the San Bernardino Mountains. The southernmost of these is struc- 

 turally continuous and open from the Mojave Desert to the Colorado River, but, like 

 the similar troughs of central Nevada, it is higher in the center than at the extremities, 



