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WALTER C. MENDENHALL 



der-colored tuff, which appears to He directly upon the metamorphic 

 rocks. Within the canyon itself and about midway of its length, 

 an exposure of the variegated lava, andesitic in character, has at its 

 base a thin bed of sandstone and conglomerate, while near the 

 mouth of the canyon the sedimentary beds rest directly upon 50 feet 

 of tuffaceous beds, which in turn overlie the older rocks. 



No effusives were observed in the Garnet Canyon section on the 

 north slope of Carrizo Mountain, but across Carrizo Creek, in the 



Fig. 4. — View down Alverson Canyon from the south slope of Carrizo Mountain. 



upper part of Barrett Canyon and especially in the ridge which 

 separates Barrett Canyon from Deguynos Canyon, just west of it, 

 is a heavy development of the lavas and tuffaceous beds. 



Here, as on the south slope of Carrizo Mountain, there is some 

 interbedding of sandstones with the flows, which evidently issued 

 contemporaneously with the beginning of Miocene sedimentation. 

 These interbedded sandstones are usually bright red or pink in hue, 

 as though partly baked by the succeeding lava stream; hence they 

 make conspicuous exposures among the more somber lavas. The 

 uppermost lava flow, upon whose upper surface lies the coral reef 

 (Fig.. 6) at the head of Barrett Creek, is about 200 feet thick, and 

 overlies a sandstone bed 20 to 50 feet thick. Below this more effu- 

 sives extend below the bottom of the arroyo. 



