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University of California. 



[Vol. 2. 



Valley. As we descend a little farther into the broad open valley 

 of upper Wildcat Canon, we find that the upper basalt escarpment, 

 which has been a persistent feature on our left to this point, abruptly 

 stops, and that the broadening out of the valley floor is coincident 

 with the expansion of the outcrop of the Siestan clays. In other 

 words, we have gotten below the level of the basalts, and we turn, 

 as we did in Siesta Valley, around the tip of a spoon-like trough of 

 these upper rocks. It is true, the tip of the spoon is not so pointed 

 as its analogue in Siesta Valley. It has the broad, blunted form of 

 a scoop rather than of a spoon, but the essential identity of the 

 stratigraphic relations in the two cases is beyond question. In the 

 water courses which traverse this broad, flat-bottomed valley there 

 arc numerous exposures of the Siestan clays and less frequent 

 but entirely satisfactory outcrops of the tuff beds. The upper part 

 of Wildcat Canon is thus, in the features described, analogous to 

 Siesta Valley, and its geomorphic expression is determined by the 

 same geological conditions. Just as we found in Siesta Valley 

 fragments and patches of basalt resting upon the clay beyond the 

 end of the basalt trough, so here we find similar residual fragments 

 and patches of basalt in a similar situation, indicating, as before, the 

 former extension of the basalt flows down the valley. In this case, 

 however, the residual patches are larger and more coherent, and are 

 mapped as a single long narrow patch. That these patches really 

 rest upon the Siestan clays may easily be proved by finding the 

 clays in place in the banks of the creeks below the thin veneer of 

 volcanic rock. 



Fossils. — In at least three places the trenching of these clays by 

 the water courses has revealed fossil logs of fairly fresh or but 

 slightly carbonized conifer timber, with bark attached. These tree 

 trunks have a diameter of from 12 to 18 inches. The wood may 

 be cut with a knife, burns readily, and shows no signs of silicifica- 

 tion such as is commonly the case with timber buried in more 

 pervious strata. In the Siestan clays to the north of Bald Peak the 

 skull of a castoroid rodent was found some years ago, by Professor 

 John C. Merriam, and described by him under the name of Sig- 

 mogompldus Le Contei* 



*This Bulletin, Vol. r, Article r, No. 13. 



