SOUTHERN PACIFIC LINES 219 
through most of Paleozoic and later time. Granite appears near the 
river bank southeast of Liberty and Buckeye. West of Buckeye the 
railroad continues along the north side of the Gila Valley, passing 
through several sidings used to some extent as shipping points for 
the many ranches in the district, most of them sustained by irriga- 
tion. Just beyond Hassayampa siding the creek of that name is 
crossed. It drains an area of moderate extent in the northern part 
of Maricopa County. There is a legend widely quoted in Arizona 
that the veracity of persons who have quenched their thiest with the 
water of Hassayampa Creek can never be relied on. Thirty miles 
to the north is the Vulture mine, on the south slope of the Vulture 
Mountains, which for a time was a notable producer of silver. The 
famous Vulture lode, discovered in 1863, yielded ore containing more 
than $4,000,000 in gold (Yearbook of Arizona, 1930). 
Not far beyond Hassayampa, near Dixie siding, there are small 
areas of recent lava, and Robbins Butte and Powers Butte, on the 
south bank of the Gila River, are conspicuous remnants of lava. In 
Powers Butte the lava caps sandstone, probably of Tertiary age. 
Here the Gila River bends sharply southward around the west end 
of the Buckeye Hills, but the railroad takes a southwesterly course. 
Near Arli n there is a small irrigation district using river water. 
Alfalfa is the principal crop, and most of it is used to feed cattle. 
Five miles south of Powers Butte, at a point where the valley is 
greatly narrowed by a lava flow,® the Gillespie Dam impounds the 
river water. This dam, built by F. A. Gillespie in 1921, is a concrete 
structure 1,800 feet long which conserves water for the irrigation of 
about 100,000 acres below Gila Bend, including the Indian reserva- 
tion that occupies a long strip of bottom lands northwest of the town. 
The geologic relations at this dam are shown in F igure 59, 
From Arlington the railroad descends into the broad valley of 
Centennial Draw, so named because it is about 100 miles in length 
from the most remote portion of the basin which it drains. The 
* The Vulture Mountains consist of 
volcanic rocks of Tertiary age lying on 
pre-Cambrian schists cut by granites 
and other igneous rocks. 
55 The lava that occupies the plain 
west of the Gillespie Dam is relatively 
recent and no doubt blocked the valley 
for a while and caused a temporary 
lake. Indistinet terraces in the Arling- 
ton Valley, especially on the edge of 
the basalt hills north of Arlington 
village, seem to indicate that the lake 
extended to that place. Probably at 
that time most of the water of the Gila 
River escaped westward through the 
pass in the Gila Bend Mountains. 
Terraces leading into the pass were 
doubtless formed then, for they could 
not have been developed by 
stream now heading in the pass. 
Gila River was probably also dammed 
by the lava flow north of Sentinel, for 
the present channel is in a gap cut 
through the lava. The west end of the 
Tint We: 
of andesitie lava interbedded in sandy 
shales and conglomerate of Tertiary 
age. The conglomerate carries angu- 
lar pebbles as much as 6 inches in 
length. 
