. Bulletin of the United States Geological Survey--Pre-Cambrian Geology of North America . Fig. 7.—Map of a part of the Colorado Valley at the northern end of the Cottonwood Valley, show-ing an old gravel-filled channel at the right and the rock channel of the river at the left. end of the basin gypsum-bearing beds similar to those near themouth of the Virgin occur with an observed thickness of severalhundred feet. U. S. GEOLOGICAL SURVE1 BULLETIN NO. 352 PL. IX. Topography fromU. S. Reclamation Service maps 200 o ?oo 400 600 800 iooo feet! w I i i i I i L_i I . I , i , , Contour interval 10 i
. Bulletin of the United States Geological Survey--Pre-Cambrian Geology of North America . Fig. 7.—Map of a part of the Colorado Valley at the northern end of the Cottonwood Valley, show-ing an old gravel-filled channel at the right and the rock channel of the river at the left. end of the basin gypsum-bearing beds similar to those near themouth of the Virgin occur with an observed thickness of severalhundred feet. U. S. GEOLOGICAL SURVE1 BULLETIN NO. 352 PL. IX. Topography fromU. S. Reclamation Service maps 200 o ?oo 400 600 800 iooo feet! w I i i i I i L_i I . I , i , , Contour interval 10 ieet MAP AND SECTION AT SOUTH END OF PYRAMID CANYON, COLORADO RIVER. DETAILS OF VALLEYS. 39 Near Round Island partly consolidated gravel beds similar ingeneral appearance to the Temple Bar conglomerate and intersectedby basalt dikes (see section K, fig. 6) occur above andesitic gravels are well stratified, tilted steeply to the east, and exten-sively eroded. Horizontally bedded Chemehuevis gravel lies indepressions eroded in older upturned beds which in turn are youngerthan the andesites. For these reasons the older gravels are pro-visionally correlated with the Temple Bar conglomerate. The Cottonwood Valley is the northernmost of a series of largebasins which extend thence southward to the Gulf of flood plain in the center of the valley is terminated laterallyby bluffs of the Chemehuevis gravel. Between these bluffs and themountai
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