. Bulletin of the United States Geological Survey--Pre-Cambrian Geology of North America . A. COLORADO RIVER AND GRAVEL-FILLED VALLEY AT BULLS HEAD B. TILTED GRAVELS IN SACRAMENTO WASH. DETAILS OF VALLEYS. 41 deep, the old one; but in the absence of soundings within the canyonnorth of Bulls Head, the depth of the new channel remains in 100 feet deep in the older channel do not penetrate throughthe gravels. A brief statement of the physiographic history of the river, ashere recorded, may give a clearer understanding of the phenomenadescribed. The river at some former time o
. Bulletin of the United States Geological Survey--Pre-Cambrian Geology of North America . A. COLORADO RIVER AND GRAVEL-FILLED VALLEY AT BULLS HEAD B. TILTED GRAVELS IN SACRAMENTO WASH. DETAILS OF VALLEYS. 41 deep, the old one; but in the absence of soundings within the canyonnorth of Bulls Head, the depth of the new channel remains in 100 feet deep in the older channel do not penetrate throughthe gravels. A brief statement of the physiographic history of the river, ashere recorded, may give a clearer understanding of the phenomenadescribed. The river at some former time occupied the old courseto the east (PI. IX) and eroded its channel to a depth considerablybelow the present river level. Later the Colorado deposited theChemehuevis gravel, filling its valley with sand and gravel to alevel several hundred feet above the present bed. When the riveragain began to erode, it feexcavated the old valley throughout thegreater part of its course, but in Pyramid Canyon, at Eagle Rock(described in the previous section), and at other places farther southto be described in following sections, it left its old course and cutrock
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