350 University of California Publications. [Geology 



ments. These lake beds are composed of semi-indurated clays, sandstones, 

 and coarse conglomerates, with interbedded sheets of volcanic tuff and 

 lava. The rocks are severely folded, the axes of the folds lying in an 

 east-west direction. The lake beds extend in the same direction across 

 the mountains for a distance of about 8 miles. It has been supposed 

 that these deposits probably continue westward under the Pleistocene 

 drift of the desert, but there is no evidence at hand to prove such an 

 assertion. In fact, the lake beds at Borate do not come down to the 

 foothills of the mountain; they are cut off and infolded with the crystal- 

 line rocks of the Calico district. Lake beds are present west of Calico 

 Valley, and a bed of colemanite has been struck in a shaft in this locality 

 at a depth of 200 feet. Although the colemanite is interbedded with 

 sand and clay, it is not coextensive with these strata. As a traceable 

 bed it probably extends for a distance of a mile and a half; beyond this 

 limit it is very thin, and in many places it is wanting in the section. 

 At the Borate mine there are two outcrops of colemanite, either on 

 parallel beds or on one bed that has been so closely folded as to give two 

 parallel layers about 50 feet apart. The beds strike approximately east 

 and west, and dip to the south from 10° to 45° . . 



Recently Keyes 11 has described the borax deposits and has 

 contributed the important observation that a lava flow overlies 

 the beveled edges of the tilted borax-bearing strata. This obser- 

 vation was confirmed during the recent reconnaissance. 



Campbell describes the beds south of the Calico Mountains 

 as follows : 



From Stoddard Wells the road follows a direct course N 20° E until 

 it emerges into the valley of Mohave Biver 5 miles west of Daggett. A 

 belt of Tertiary rocks having a width of about 1% miles is crossed by 

 the road 4 miles south of this bend. The rocks are composed generally 

 of fine clay and sand, containing a large amount of gypsum and other 

 salts. Several thick beds of limestone were noted, which appear to have 

 been the result of chemical deposition. The lower beds are composed of 

 fragmental material; but in the upper part of the series occur many lava 

 sheets which preserve the beds in high, even-crested ridges. This belt 

 of rocks extends in a nearly east-west direction. The strata have been 

 gently tilted along an axis running in the same direction, so that they 

 now dip to the north about 5°. 



The ridge formed by these beds appeared to extend westward for a 

 distance of only a mile or two, and then to die out in the even expanse 

 of desert which presumably extends to Mohave Biver. Toward the east 

 the lake beds extend indefinitely. The question of the relation of these 

 beds to the horizontal strata west of Mohave Biver is most interesting, 

 and an examination of the western end of the beds just described might 

 throw light on the relative age of these deposits. 



" Borax deposits of the United States, Trans. Am. Inst. Min. Engrs., 

 no. 34, pp. 867-903, 1909. 



