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University of California. 



LVol. 3. 



way of Toowa Valley from the southern end of the plateau, has 

 no inherent objection, and by elimination of the other two possi- 

 bilities seems the most probable hypothesis. In this event the 

 drainage either followed Toowa Valley eastward to a gap in the 

 summit crest, shown in Plate 35 a, and thence out into the region 

 of the Great Basin at the south end of Owens Lake, or it turned, 

 following the course of the South Fork, and joined with the high 

 valley represented by Little Kern Plateau, lower down on the 

 Kern. Unfortunately for the decision of this alternative, the 

 writer has no knowledge of the country traversed by the South 

 Fork after it leaves Toowa Valley; but the extensive Monache 

 Meadows indicate that the South Fork traverses a valley which 

 has characters similar to those of Toowa Valley, and, if this be 

 true, then the ancient drainage probably followed that line. 



With the rapid downcutting of Kern Canon, under the above 

 hypothesis the upper part of Toowa Valley was beheaded and 

 the drainage of its upper part reversed. This reversed drainage 

 may have extended at one time farther up Toowa Valley than at 

 present. Whether this be so or not, the segregation of the 

 drainage into two streams, Volcano Creek and South Fork, 

 is, so far, at least, as the determination of the place of segrega- 

 tion is concerned, an accident due to aggradation caused by 

 volcanic damming of the valley. 



The fact that the Kern abandoned the Toowa Valley route 

 after the uplift may be explained on the supposition that the old 

 route, under the new conditions of erosion, was too roundabout 

 to compete with the shorter course, and that a cut-off was effected 

 by a short tributary of a lower part of the Kern capturing the 

 main drainage. 



THE CANON ZONE. 



The canon of the Upper Kern is one of the great canons of 

 the Sierra Nevada; and in some respects it is the most remark- 

 able of them all. It represents the most recent dissection of the 

 high mountain mass in consequence of an uplift which raised the 

 floor of the High Valley system far above the base level of 

 erosion, and so caused the streams to sink deep trenches in that 

 floor. But while it is a feature essentially due to stream erosion, 

 its characters as such have been modified by its having been 



