102 DESCRIPTION OF SODA LAKE. 



form ; bounded on the east by the elevated aud mountain range formed of granitic and porphyry 

 uplifts which separate the Mojave valley from that of the Colorado, and on the west by the con- 

 glomerate slopes of the ridge just described. The surface of the playa is perfectly level and 

 without vegetation, save on the margin, where some coarse salt grass flourished in the loose 

 sands ; on the edge of these sands could be traced a beach — heaped water-worn pebbles, pieces 

 of drift wood, and vegetation — and for miles the eye could trace this dark line at the base of the 

 small sand hills accumulated by the winds ; yet at the time of the visit (April 14) there was no 

 water over the surface, nor has it ever been known as a permanent lake. For several hundred 

 yards from the margin the soil, a sandy clay, was hard and ripple-marked, and coated from 2 

 to 1 inches deep with a saline incrustation which crackled under the feet like frozen snow ; 

 examined by the eye it contained cubes of common salt, had an alkaline taste, and deliquesced 

 in the fingers ; it raised bread indifferently well, and was therefore a mixture of cloride of 

 sodium and carbonate of soda; an analysis of this eSlorescence is subjoined. Further in, towards 

 the centre of the playa, dry stream beds exist 2| to 3 feet below the general level, and about 5 

 yards wide ; and in the neighborhood of these the soil is a quicksand, which, though supporting 

 a man who shifts his position occasionally, renders it very unsafe for a mule to keep its foot, the 

 animal frequently sinking to its belly. In this playa the Mojave river is finally received ; its 

 course down the conglomerate being visible for some miles, when it gradually sinks down and 

 disappears in toto. The whole under stratum is soaked with its waters. Digging at the edge, 

 18 inches deep, allowed abundance of water to ooze in, sufficient for culinary purposes, but 

 which requires to be used fresh, as, after it has lain some hours, it becomes intolerably saline; 

 at the best it is mawkish and alkaline, and only to be drank on necessity. Occasionally the 

 playa is overflowed with water and forms a small lake, whose margin or beach has just been 

 described ; it is never more than a few inches deep, and drying off again leaves the alkaline 

 incrustation on the surface. 



The playa is nearly divided into two portions by a projecting ledge of trachytic porphyry, 

 which has in immediate contact with it a mass of primary limestone, forming a hill about 500 

 feet high ; at the foot of this is a small fresh water spring of remarkably pure hard water. The 

 limestone is metamorphosed, and presents no trace of fossils ; it probably is geologically con- 

 nected with the limestones of the Sierra Nevada, and that in the vicinity of the bay of San 

 Francisco, along the Santa Cruz valley. 



The aspect of the playa is remarkably forbidding ; a wide expanse, unclad with herbage, 

 bounded by lurid purplish hills without timber, smooth as a bowling green, and glittering in the 

 sun like a snow field, dry brown slopes rising to the margin of the rocks, forms a most dismal 

 picture, and gives an idea of incompleteness and desolation. 



The mirages on this playa were constant, and on a very large scale. 



The formation of so large a crust of salt and alkaline carbonate from the capillary evapora- 

 tion of the soil of the playa shows how large a quantity of mineral matters may be abstracted 

 by running water percolating through porous sandstones and the debris of albitic granite ; for 

 the waters of the Mojave were, in the first instance, merely the melted snows of San Bernardino ; 

 all the mineral matter, therefore, in its volume, were derived from the strata along which it 

 rolled, concentrated by accumulation in Soda lake ; for in no part of its course was the flowing 

 river at all saline, or unpalatable to the taste. 



