54 BULLETIlSr 54, U. S. DEPARTMENT OF AGBICULTURE. 



arc not uncommon, and, c. pecially in the San Joaquin, shallow local 

 depressions have become small inclosed basins or lakes like Kern and 

 Tulare, which overflow only at times. Here, as in the Great Basin, 

 evidences of stream decay are everywhere. None of these local basins 

 are structural, none have walls high enough to be even directly per- 

 ceptible, and none have any significant antiquity. The saline accu- 

 mulation gets no further than the formation of "alkali" soU, and has 

 no significance to the present inquiry. 



THE PILLED LAKES OF THE CALIFORNIA RANGES. 



In the mountains of these ranges, as of most others, are many small 

 depressions which are or have been filled by lakes. In the course of 

 time these lakes have been slowly filled by alluvium, and at the same 

 time their outlets have been slowly lowered by stream corrasion, 

 until at last the rising alluvium met the falling water surface and the 

 lakes have become flat-filled valleys with a more or less vigorous 

 original or through-flowing drainage. Examples of this process, 

 locally modified, have already been mentioned — the Antelope Valley 

 in Oregon (p. 25), the Smith Valley in Nevada (p. 18), and the 

 Tehachapi Valley in California (p. 42). Literally hundreds of others 

 in all stages of development may be found in the Sierra, the Coast 

 Range, the Cascades, and elsewhere. Plate I, fig. 1. 



Where the drainage is sufficiently vigorous, either because through- 

 flowing or for some other reason, these filled lakes do not interest us. 

 In many cases, however, an original drainage, never very vigorous, 

 has not been able to maintain itself and has been imprisoned within 

 the valley. . Probably the most extreme instance of this is the basin 

 of the Carriso Plains in the southeastern corner of San Luis Obispo 

 County, Cal.^ Nearly 500 square miles of this valley, once tributary 

 to the San Juan Creek, have been cut off by alluvial deposition and 

 stream decay probably complicated by local movement, and have 

 developed an internal drainage concentrating in Soda Lake, which is 

 now a playa saturated with a strong salt solution in which sodium 

 sulphate predominates. Of course this condition is quite recent, 

 and, from the present viewpoint, quite unimportant. 



THE BASINS AND PONDS OF THE COLORADO PLATEAU. 



The northern third of Arizona, the northwestern quarter of New 

 Mexico, and adjoinmg portions of Utah and Colorado make up the 

 Great Colorado Plateau. Subjected to some movement and consid- 

 erably dissected by the Colorado and its tributaries, this plateau 

 nevertheless retains wide areas in which reUef is small and slope 

 imperceptible, and over which drainage is at best sluggish and uncer- 

 tain. These areas have suffered greatly from the prevalent desicca- 



• Arnold and Johnson, U. S. Geol. Sur., Bui. 880, 369 (1909). 



