210 GUIDEBOOK OF THE WESTERN UNITED STATES 
From Safford northwest the railroad follows the southwest side of 
the Gila River, passing through an extensive irrigation district about 
the towns of Thatcher, Central, Pima, and Fort Thomas. In this 
region are many remains of dwellings and pottery of aborigines who 
used the water of the Gila River for irrigation many centuries before 
the coming of the white man. To the north is the high ridge of the 
Gila Mountains, made up of great flows of lava and deposits of vol- 
canic tuff, agglomerate, and ash extending north to the White Moun- 
tains, which were the center of eruption of a vast amount of volcanic 
matter in Tertiary time. To the west are many high mountains con- 
sisting mostly of granite of pre-Cambrian age. About 11 miles north 
of Pima are hot springs, probably rising along a fault at the foot of the 
Gila Mountains. At Fort Thomas was an old frontier fort. At 
Geronimo the route enters the San Carlos Indian Reservation, 55 
miles wide and occupied by 2,715 Apache Indians, a district of valley 
and mountains with considerable good land along the wide alluvial 
flats adjoining the Gila River. The lower part of the valley in the 
center of the reservation, however, is flooded by the great San Carlos 
Reservoir created by the Coolidge Dam, which is built in a narrow 
canyon in the Mescal Mountains. The dam, completed in 1927 at a 
cost of $5,500,000, was constructed by the United States Commissioner 
of Indian Affairs to control water for the irrigation of the Gila River 
Indian Reservation and the adjoining region west of Florence and 
about Coolidge, Casa Grande, and Sacaton. According to the records 
in the office of the Commissioner the dam, which is of novel construc- 
tion, consists of three domes supported by two buttresses, is 250 feet 
high and 920 feet long, and has a spillway capacity of 120,000 second- 
feet. The reservoir is about 25 miles long and in places 4 miles wide 
and has a capacity of about 1,200,000 acre-feet of water. Thisamount 
is sufficient to cover 100,000 acres to a depth of 12 feet, which is four 
times the volume required for one year’s irrigation in the Casa Grande- 
Gila Reservation region. Below the dam is a power plant using two 
7,500-horsepower turbines. This dam is barely visible from the rail- 
road, which now skirts the north and east margins of the reservoir, 
but it is crossed by the highway from Bowie to Globe. At its abut- 
ments are fine exposures of eastward-dipping limestones of Carbonif- 
erous age. 
San Carlos, long known as Rice, is at the confluence of the San 
Carlos River and Aliso Creek, two streams which also supply water 
Sins Cabten, to the San Carlos Reservoir. On both sides of the 
Elevation 2,623 feet, Valley here are lava-capped mesas, and a short dis- 
Population 43, tance east is the old volcanic vent known as the 
-< Oreans 1449 Triplets. From San Carlos the valley of Aliso Creek 
poe is ascended. To the south are the high granite 
_ Tidges of Hayes Mountain, capped in part by an extensive succession 
a 
