4H 



University of California. 



[Vol. i. 



section from the town of Stockton, which lies somewhat west of the 

 middle line of the valley, to Pyramid Peak, near the crest of the 

 Sierra. The section is not carried across the whole valley, as obvi- 

 ously only the eastern half of the latter could have been effectively 

 concerned in elevating the Sierra Nevada crust-block, while the 



P»,„,.,j Pi 



western half was performing a similar office for the Coast Ranges. 

 For the sake of simplicity, the general slope of the Sierra is carried 

 down in a straight line under the valley sediments, reaching a depth 

 of about 4,500 feet under Stockton. If we assume that this is the 

 thickness of the sediments which were effective in causing elevation, 

 then the diagram shows the great disparity between the effect and 

 the supposed cause. But it may be that the subsiding valley sedi- 

 ments are much thicker than this, in which case they would have 

 to attain a thickness of nearly 20,000 feet to become an effective 

 counterweight to the Sierra mass. It is barely possible that the 

 total undisturbed strata of post Jurassic age may attain a thickness 

 of 20,000 feet beneath Stockton, but by no means all of these could 

 be regarded as available for initiating the elevation of the Sierra in 

 Pliocene times, that being the date Mr. Becker assigns to the faults. 

 For this would imply a storing up of energy since the opening of 

 the Cretaceous, whereas it is very improbable that any such pent- 

 up forces should have failed to find relief in isostatic readjustment 

 during the vigorous orographic movements at the close of the 

 Miocene. 



Thus far the discussion has been limited to the Great Valley 

 and its immediate hydrographic basin, but the parallelism of the 

 former with the numerous smaller valleys of the state, and with the 

 larger one of the Gulf of California, is so striking, and so suggestive 

 of genetic relationship, that it seems better to treat of it at this place, 

 rather than in the general discussion later on. Such a general 

 parallelism between coast line, mountain ranges, and valleys can mean 

 only one thing, viz., that the latter have been formed or determined 



