TOPOGRAPHY OF THE PACIFIC COAST. 53 



If, when thus mantled with residuary material, the Sierra 

 Nevada region were affected by a change of level in such a way 

 as to slightly increase the fall of the streams upon its slopes, it is 

 believed, as already suggested, that during a comparatively brief 

 period owing to overloading they would be forced to deposit and 

 fill their channels. A portion of the process is, in a measure, 

 illustrated by what has taken place along some of the present 

 streams of the Sierra Nevada where hydraulic mining has been 

 extensively carried on. The streams are overloaded by the 

 debris forced into them from the mines and their channels are at 

 least temporarily filled with gravel. 



After the deposition of the earlier gravels the declivity of 

 some of the streams at certain points appears to have been so 

 decreased that they deposited finer material and covered the 

 gravel with sand and clay. This may have resulted from differ- 

 ential elevation, differential subsidence, or both, and there is 

 evidence that both occurred within the gravel period. At Cherokee 

 Flat upon the eastern border of the Sacramento valley the finer, 

 essentially estuarine deposits, over 300 feet in thickness, lap over 

 to the eastward upon the ancient river and shore gravels mined 

 at that place. This overlapping evidently resulted from a subsi- 

 dence of that region. " 



SUMMARY. 



A study of the ancient topographic features upon the bor- 

 ders of the Sacramento valley, in the Klamath Mountains, and 

 upon the western slope of the Sierra Nevada, shows that during 

 the earlier portion of the auriferous gravel period, southern 

 California, by long continued degradation, was finally reduced 

 approximately to baselevel conditions. The mountain ranges 

 were low, and the scenery was everywhere characterized by 

 gently flowing slopes. 



The distribution of the lone formation and the early aurif- 

 erous gravels, as well as the plant remains which they contain, 

 point clearly to the same conclusion. 



The topographic revolution consisted in developing out of 

 such conditions the conspicuous mountain ranges of to-day. 



