12 



Sierra Club Bulletin. 



Although nothing now remains of ancient Lake Yosemite, 

 its extent, nevertheless, is still easily ascertained. One need 

 but follow the edge of the level meadows that now form the 

 valley floor, in order to trace the former shore line. Evidently 

 the lake occupied the entire extent of the valley, up to the cliffs 

 that enclose its head; its length, therefore, must have been 

 close to six miles. 



Nor was it a mere shallow pool. Its depth, there are reasons 

 for believing, may have exceeded 500 feet. No actual measure- 

 ments, such as might be obtained by borings, for instance, are 

 available, it is true, and the figure mentioned cannot claim to 

 be any more than a mere estimate. Yet it is not wholly without 

 foundation, as a glance at the accompanying diagram will show. 

 That diagram represents one of a number of cross-sections of 

 the valley, constructed by the writer with the accurate and 

 abundant trigonometric data on which the detail map of the 

 Yosemite Valley is based. Being free from vertical exaggera- 

 tion, it affords a fair means for judging the probable depth of 

 sediment now filling the valley. It is reasonable to assume that 

 the Yosemite Valley, having been vigorously glaciated, pos- 

 sesses a somewhat concave rock floor, shaped like the bottom 

 part of a U. Completing, tentatively, the missing part of the 

 curve, therefore, one obtains an approximate measure of the 

 depth of the extinct lake. In the cross-section published here- 

 with, the curve has purposely been drawn quite flat, in order that 

 the estimate of depth may not be accused of undue liberality. 

 Yet, the depth indicated by the diagram is not far from 500 

 feet. Other cross-sections give closely accordant figures, those 

 toward the head of the valley indicating still greater depths. 



Is it to be inferred also, the question may here be asked, that 

 the El Capitan moraine has a height of 500 feet? No, that 

 ridge, in all probability, does not stand a hundred feet high 

 above its base. A direct measurement of its height, unfortu- 

 nately, cannot be had. The river has not yet cut the notch down 

 to bed rock. At least so Galen Clark informed the writer. 

 While still in charge of the valley, he had undertaken to enlarge 

 the notch in order to lessen the danger from floods during the 

 spring freshets. He had found only loose boulders, which he 

 had removed with the aid of dynamite. 



