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 isnow changed. Perhaps more than any other 
American area the Mojave Desert shows the effects of lessened rainfall. Itisa 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 evéry 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, but this 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*in 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 alsoin 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 he 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, — 
