28 RECONNAISSANCE OF PART OF WESTERN ARIZONA. 
canyon. The unnamed hills north and south of the central mass are 
remnants of erosion, now separated from the main peak by debris- 
covered passes. 
Rock masses. — With the exception of The Needles, the rocks of the 
Mohave Mountains, so far as observed, are granite, gneiss, and later 
intrusives. The crystallines have been greatly fractured and faulted 
and contain many dikes and veins. The extrusive rock of The Nee- 
dles overlies the crystalline complex on the eroded flanks of the 
Mohave Mountains, and is exposed in the canyon down to the river 
level. The thickness of the effusive rock as measured from the river 
bed to the summits of The Needles is about 2,000 feet. 
HARCUVAR AND HARQUAHALA MOUNTAINS. 
Location. — The Harcuvar and Harquahala mountains are located 
in the southern part of the area described, and extend from the 
eastern border of this area about 50 miles in a general southwesterly 
direction. They resemble each other in many ways and may be 
described together. 
Topographic features. — The axes of these mountains lie in a direc- 
tion practically at right angles to' those of the other ranges of the 
region. Next to the Hualpai Mountains they are the loftiest in cen- 
tral western Arizona. 
Both ranges are narrow, with precipitous slopes rising abruptly 
to altitudes of several thousand feet above the graded plain which 
surrounds them. The main range of the Harcuvar Mountains is 
broken at Cunningham Pass, and at either end the ranges break up 
into isolated hills. At the west end of these mountains a group 
known as the Granite Wash Hills exhibits a tendency to return to 
the north-south trend characteristic of the other ranges of western 
Arizona. 
Rock masses. — The rocks were observed only in Cunningham Pass 
in the Harcuvar Mountains and near Harrisburg in the Harquahala 
Mountains, where they consist of a crystalline complex underlying 
and to some extent including masses of quartzite, argillite, and meta- 
morphic limestone. A few miles south of Harrisburg, where these 
sediments were examined most closely, the strata stand nearly 
vertical. 
BUCKSKIN MOUNTAINS. 
Location. — The Buckskin Mountains, lying immediately south of 
Williams River, are virtually the southward continuation of the 
Aubrey Hills, being separated from them only by the narrow gorge 
cut by Williams River. 
Topographic features. — The Buckskin Mountains are lofty at their 
eastern extremity, with a precipitous slope facing southward. The 
