SOUTHERN PACIFIC LINES 215 
At the dam are great rock walls exhibiting one of the finest known 
sections of the Apache group, which lies on pre-Cambrian granite and 
is overlain unconformably by sandstones and limestones of Cambrian, 
Devonian, and Carboniferous age. (See fig. 57.) The strata dip 
eastward, and the hard quartzites form the crest and east slope of a 
high mountain range, the northern part of which is known as the 
Mazatzal Mountains (mah-zat-zahl’, Indian word for red rocks). 
The river has excavated a canyon nearly half a mile deep across this 
range, which has been uplifted since the stream has flowed in its 
resent course." The range is a long up-tilted block of the earth’s 
crust, west of which the pre-Cambrian rocks occupy a wide area, in 
part overlain by Tertiary volcanic rocks. 
Below the Roosevelt Dam the road descends the Salt River Canyon 
along its south side, crossing a wide area of the old granite that under- 
69y , 
SW. = Sonn oy NE: 
J 
Rh . esther at?) 
a Tine (iE 
FIGURE 57.—Section at Roosevelt Dam, Ariz. 
lies the Apache group near the dam. In places, especially at points a 
few miles west of the dam, this granite is invaded by thick dikes of 
5t The section begins a short distance | feet. Much of this limestone is 
below the dam and extends to the | but some beds contain considerable 
quarries southeast of the dam. The | interbedded chert in thin layers, pos- 
and the Scanlan conglomerate, the | lies a sheet of lava (basalt), vesicular 
basal formation of the Apache group, | in large part, especially at the top and 
is clearly exposed on the road as well le. 
as in the north wall of the canyon, a | This was a surface lava flow in late 
short distance below the dam. The | Apache time. The overlying sand- 
Dripping Spring formation, next above, | stone (Cambrian), about 200 feet 
is a reddish quartzite, in part slabby, | thick, contains at the base pebbles of 
but so hard and compact that it makes | the lava and other rocks, and though 
the mountain crests to the north and | conformable in attitude it is separated 
the Mescal limestone, which here | which are well exposed in ledges and 
attains its maximum thickness of 350 | quarries above the dam, 
