SOUTHERN PACIFIC LINES 233 
wind and accumulated at the foot of the slope. Farther north, near 
the railroad, this pediment is deeply trenched by small arroyos. At 
the north end of the Mohawk Mountains is the Gila River; at this 
place Garcés in 1775 crossed to the south side of the river. The 
Mohawk Mountains were named Cerro de San Pascual by Anza on 
his expedition of 1774; he camped at their north end the following 
year. 
West of the Mohawk Mountains is the wide desert plain of Mohawk 
Valley, which extends west for about 15 miles to a line of ridges con- 
sisting of the lava-capped Cabeza Prieta Mountains (cah-bay’sa 
pre-ay’ta, Spanish for black head), to the south; the Copper Moun- 
tains, a conspicuous rugged range of granite southwest of Colfred 
siding; and the Baker Peaks, a short distance south of Tacna siding. 
The prominent Baker Peaks, named for Charles Baker, who in early 
days ran a ferry across the Colorado River at Yuma, consist of tilted 
sandstones presumably of Tertiary age.” South of the Baker Peaks 
are ridges of conglomerate, also of Tertiary age, extending to the 
flank of the Copper Mountains. Far to the north are the fantastic 
summits of the Castle Dome Mountains. Closer at hand to the 
northeast from Colfred siding is Signal Butte, rising prominently 
above the desert plain a scant 5 miles beyond the Gila River. Itisa 
small mass of basalt probably marking the center or outlet of a minor 
lava extrusion. 
A mile north of Tacna siding and extending for a mile to the bank 
of the Gila River is Antelope Hill, about 600 feet high. It consists of 
grayish arkose composed largely of granite débris and probably of 
Tertiary age. The dip is to the south at a low angle, and about 500 
feet of beds are exposed. There are also small exposures of this rock 
in smaller buttes just north of the railroad 2 miles farther west, in 
which the dip is 15° SW., and another small exposure northeast of 
Antelope Hill. The material has been quarried extensively, mainly 
for road metal. 
At Wellton the old main line of the railroad is joined by the new 
line from Picacho by way of Phoenix. (See p. 223.) 
inches to 3 feet in diameter. The 
+ to} + + tiar tna iA $4 nk 
6&3 These rocks are well e: d at 
Baker Tanks, 5 miles south of Tacna, 
where the conglomerate dips 65° SW. 
by present streams on the slope of 
beds are a coarse conglomerate with 
many pebbles and boulders from 3 
152109°—33——16 
Baker Peaks as to indicate that it was 
derived from the same rocks under con- 
ditions similar to those which now 
exist. 
