38- 
RECONNAISSANCE OF PART OF WESTERN ARIZONA. 
which is known as the Cottonwood Valley. The basin is about 30 
miles long and extends laterally from the Dead Mountains on the 
west to the Black Mountain Range on the east. At the northern 
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 the 
mouth of the Virgin occur with an observed thickness of several 
hundred feet. 
