3l8 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



Tenaya Canyon are massive and do not suggest extensive 

 faulting. A graben with a depth of 4,000 feet would 

 probably have a much greater longitudinal extent than the 

 length of Yosemite Valley. 



4. We are now brought down to the fourth hypothesis, 

 which would place the Yosemite in the same category with 

 the other rugged and deep canyons of the Sierra. The fact 

 that Hetch-Hetchy Valley was initiated in Tertiary time has 

 already been noted. While we have no positive evidence, 

 this is likewise probably true of the Yosemite, for nearly all of 

 the rivers of the southern Sierra Nevada appear not to have 

 been filled with lavas and displaced during the late Tertiary, 

 as was the case farther north. There may thus have been 

 a river valley on the site of the present Yosemite in the 

 beginning of the Pleistocene, and this valley may easily 

 have been a thousand feet deep at that time. This lessens 

 the difficulty of accounting for the present depth of the 

 Yosemite and of other canyons of the southern Sierra. 



If Yosemite Valley were unique, some special origin 

 might be sought for it. As a matter of fact there are 

 several valleys in the Sierra Nevada similarly situated and 

 sufficiently similar in configuration to suggest that they all 

 originated in the same manner. As has been noted by Le 

 Conte and others, these valleys lie in about the same posi- 

 tion relative to the crest of the range. Le Conte refers to a 

 valley near Sugar Loaf on the South Fork of the American 

 River (Pyramid Peak quadrangle) as being comparable to 

 the Yosemite. A small valley on the Middle Stanislaus 

 at the mouth of Niagara Creek (Dardanelles quadrangle) 

 has precipitous walls and a narrow outlet. Mr. Becker has 

 referred (loc. cit., p. 35) to a gorge which seems to him an 

 incipient Yosemite. Another canyon which under favorable 

 circumstances would widen out into a Yosemite is the lower 

 part of Sawmill Canyon (See Plate XXXVIII). The granite 

 is here divided into a number of vertical sheets by an east 

 and west joint system, and along these joints vertical cliffs, 

 over 2,000 feet high, have formed. This was the work of a 

 small stream aided by heat and frost, for the glacier that 



