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University of California. 



[Vol. 3. 



top of the cinder cone on the divide between Volcano Creek and 

 the South Fork, Toowa Valley is for the most part a rocky plat- 

 form of subdued, rolling relief, which forms a distinct terrace 

 above the meadows which wind through it. This is the second 

 stage of the valley floor. It is the breadth of this feature which 

 gives the valley its expansive character. The flat bottom lands 

 are a subordinate feature. This upper stage of the valley floor 

 is more or less dissected, but in its general aspect it is a rocky 

 surface of very gentle rise to the sides of the valley, where it 

 merges by transitional slopes into the upland from which the 

 valley has been carved. The altitude of the terrace ranges from 

 about 200 feet to perhaps 600 feet above the bottom lands of 

 the valley, but lower spurs run out from it into the meadows. 

 Views of the valley are given in Plates 35 a and 36 a, b and c. 



Toowa Valley, as represented by the upper stage of its floor, 

 is evidently a very mature erosional feature. The character of 

 the surrounding mountains is in harmony with this conclusion. 

 While the country might still be described as rugged, it lacks 

 the fierceness of the glaciated mountains to the north. The 

 ridge profiles are characterized by a flowing rotundity; there is 

 an entire absence of deep shear-wall canons and of sharply ser- 

 rate crests and pinnacles; the flaring V-shaped side valleys widen 

 noticeably as they approach the master valley, and the crest 

 lines of the divides between these side valleys have a marked slope. 

 (See Plates 35a and 36 a, b and c). The maturity of this broad 

 transmontaine valley is analogous in degree to that of the 

 Chagoopa Plateau, it lies in the same hypsometric zone, and is 

 separated from it by no barrier and by no break except the canon 

 of the Kern. We may, therefore, with great confidence and with 

 little chance of error, correlate the two features as slightly dif- 

 ferent phases of the High Valley system of this portion of the 

 Sierra Nevada. The aggraded bottom lands of Toowa Valley 

 represent a dissection of this high valley, and if this aggraded 

 product were removed we should doubtless find beneath it a fairly 

 incisive canon due to a relative lowei'iug of the base level, and this 

 depression of the base level may reasonably be referred, as will 

 appear a little later, to down cutting of the canon of the Kera, 

 the master stream of the region. 



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