40 
RECONNAISSANCE OF PART OF WESTERN ARIZONA. 
the detailed maps do not extend far enough northward to show to 
advantage the relation of the new roek channel to the old gravel-filled 
valley, but its southern end is shown in PL IX, and its relations 
are indicated in fig. 8. In PL X, A, a view of Bulls Head rock is 
presented, showing the river channel to the left and the gravel-filled 
valley to the right, as seen from the south. At intervals for several 
miles north of Bulls Head rock the ridge between the old and new 
channel is cut through by tributary washes, exposing such sections 
of the Chemehuevis gravel as that shown in PL III, B. 
The old course was not so satisfactorily traced to the south. 
As shown on the map, it apparently crossed the present course of the 
river at a point where the gravels fill a depression similar to that at 
Fig. 8.— Profiles across Colorado River at the southern end of Pyramid Canyon, constructed from 
boring records. (For location see PI. IX.) 
the north, and connected with the extensive gravel deposits of the 
Mohave Valley to the south. 
Although the river occupies a narrow rock channel in Pyramid 
Canyon, it does not flow upon a rock bed, as might be expected. 
Borings were made for the Reclamation Service in three localities 
across the river (see PL IX), and the gravel filling was found to be 
more than 100 feet deep. The probable profiles, as constructed 
from the boring records, are shown in fig. 8. 
No distinction can be drawn with certainty between the old and 
new channels at the places where the borings were made. At the 
northernmost locality (section A-B, fig. 8) the channel at the left now 
occupied by the river, in which the gravels are about 50 feet deep, 
is apparently the new one, and that at the right, more than 100 feet 
