GEOLOGIC RECONNAISSANCE OF A PART OF 
WESTERN ARIZONA. 
By Willis T. Lee. 
INTRODUCTION. 
Purpose of the investigation. — The investigations described in this 
bulletin were made in western Arizona under the general direction 
of Mr. N. H. Darton. The region examined lies mainly west of the 
high plateau and north of latitude 33° 30\ 
The original purpose was to investigate the water resources of the 
region and the extent to which they might be developed. This 
necessitated an examination of the geographic features with special 
reference to irrigable lands and the possibilities of getting water to 
them, and of the geologic formations with reference to their bearing 
on questions of underground water. Conditions were found so unfa- 
vorable for water development in this region that the economic results 
of the work are unimportant, or at best have negative value. On 
the other hand, the region proves to be one of great geologic interest. 
Many significant features were observed, and their bearing on impor- 
tant geologic problems was noted, but want of sufficient time as 
well as the desert condition of the region made it impossible to fol- 
low out many of the most interesting lines of investigation. 
Extent and character of the investigation. — The observations were 
made during rapid reconnaissance trips. In the summer and autumn 
of 1903 the Hualpai, Detrital-Sacramento, Big Sandy, Chino, and 
Aubrey valleys were visited, and Colorado River was examined from 
Needles, CaL, southward to Yuma, Ariz., the object of the river trip 
being to examine the geologic conditions at the various reservoir 
sites of the Reclamation Service along lower Colorado River. Dur- 
ing the spring and summer of 1904 a more extended reconnaissance 
was made, including a river excursion from the mouth of Grand Can- 
yon to Needles, CaL, and several overland trips shown on the accom- 
panying map (PI. I). 
The amount of territory covered necessitated for the most part 
very general observations, and as the investigation was undertaken 
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