DETAILS OF VALLEYS. 
43 
eral the rock walls rise abruptly from the waters edge, but in sonic 
of the more open spaces sand and gravel of the Chemehuevis forma- 
tion occur to a considerable height above the river. 
At Big Bend, 4 miles south of Mellen, the river leaves a compara- 
tively open portion of the canyon and turns abruptly to the west 
into a narrow rock gorge having an old gravel-filled channel, which 
continues southward in the normal direction of the river (fig. 10). 
Fig. 10.— Mapof Greal Bend in Mohave Canyon, showing relation of an old debris-filled channel to 
the present course of Colorado River. 
The phenomena here are similar to those just described from Pyramid 
Canyon, except that the new course is shorter and the gravel filling 
of the old one has been more nearly eroded away than in Pyramid 
Canyon. 
CHEMEHUEVIS VALLEY. 
The Chemehuevis Valley extends from The Needles to the mouth 
of Williams River, a distance of about 25 miles, and is narrower than 
