24 



DYNAMICAL GEOLOGY. 



advent of man. The displaced rivers have since that time 

 cut new channels, far deeper than the old, so that the old 

 lava-covered channels are high up on the present divides 

 (Fig. 6). Thus, in very recent geological times i. e., in 



FIG. 6. Section across old and new river beds of California, r, r, new river beds ; 

 r\ old river bed; gr, gravels of present rivers; gr', old river gravels; dotted line, 

 old configuration of surface. 



the Quaternary and present epochs water has cut at least 

 2,000 feet deep in hard slate-rock. 



We have selected these cases because of the plain evi- 

 dence of recent work, but the whole western slope of the 

 Sierra is trenched with enormous ravines, 3,000 to 6,000 

 feet deep, although the history of some of them is longer 

 than those spoken of above. For example, commencing 

 north and going southward, we have the Columbia River, 

 with its gorge 3,000 feet deep in hard lava. The branches 

 of the Feather, Yuba, and American Rivers have cut 

 gorges 2,000 to 3,000 feet deep in hard slate. These have 

 the structure represented by Fig. 6, and have been cut 

 wholly in very recent geological times. The Tuolumne 

 and Merced Rivers have cut gorges 3,000 to 5,000 feet 

 deep, the famous Hetch-hetchy and Yosemite Valleys 

 being in the course of these. King's River Canon is 

 7,000 feet deep, in hard granite. 



Plateau Reg-ion. But the most wonderful gorges or 

 caflons in the world are found in the high-plateau region 

 i. e., the region between the Colorado and Wahsatch 

 Mountains, and drained by the Colorado River. This 

 region is 6,000 to 8,000 feet high, and consists of nearly 



