36 GLACIAL AND SURFACE GEOLOGY OF THE PACIFIC COAST. 



frequent occurrence, and which may be mistaken for glacial phenomena by 

 inexperienced observers. The peculiar weathering of the granite outcrops 

 in the Sierra has been repeatedly mentioned in the Geology of California, 

 and need here only be recalled to mind as the cause of many misconcep- 

 tions. Some ridges, as, for instance, one on the north side of the Temescal 

 Range,* are covered with rounded masses of rock, which at a little distance, 

 and without close examination, seem to be unquestionably drift boulders. 

 They are, in point of fact, the remains of the disaggregation by weathering 

 of the concentrically laminated granite, as is easily recognized, when it is 

 observed that the rock may be found in all stages of passage from the ahnost 

 solid ledge, faintly marked with concentric bands of color and fine lines 

 or cracks, up to the entirely detached and boulder-like masses which rest 

 on the surface, as if brought from a distance and deposited there by ice or 

 water. Sometimes, however, the granite, instead of assuming regularly 

 rounded forms, takes on the most fantastic shapes. A locality of this kind 

 may be seen near Lone Pine, in the valley of Owen's Lake, along the west 

 side of the so-called Virginia Hills. 



Another source of error, especially apt to be met with in the ranges of 

 mountains of the southern part of California, is found in tlie way in which 

 detrital materials have often been carried down the canons, entirely beyond 

 the edge of the mountains, and spread out on the adjacent plains. This 

 kind of occurrence has already been described in the gravel volume in 

 speaking of the great " washes " at the base of the high ranges. It need 

 only here be noticed that such washes always spread out fan-shaped from the 

 mouth of the canon from which they issue, while true moraines as inva- 

 riably lie in parallel lines. The former also always present in a cross section 

 parallel with the range a nearly uniformly rounded surface, the highest 

 portion of which is directly opposite the mouth of the ravine ; moraines, on 

 the contrary, exhibit evidence of having been piled up on each side of an 

 advancing mass of ice, in that they form two very distinct lines of accumu- 

 lated material, with a deep depression between them and opposite the centre 

 of the caiion. 



As already mentioned, the Sierra falls off" very rapidly in elevation, from a 

 jioint about opposite the lower end of Owen's Lake. The range here con- 

 sists of three principal parallel branches, having the continuation of Owen's 

 Valley, south of the lake of that name, on the east, and Tulare Valley on the 



* See Geology of California, Vol. I. p. 179. 



