DETAILS OF HIGHLANDS. 21 
Cliffs exhibit the characteristic features of an erosion escarpment, 
the steep face being maintained by the hard Redwall limestone at 
the top. 
Rock masses. — Pre-Cambrian granite occurs in the base of the 
cliffs. It was observed by the writer in four localities — at Music 
Mountain, in Truxton Canyon, near Cross Mountain, and at the 
southern end of the Juniper Mountains. As in the Grand Wash 
Cliffs, it terminates above in a base-leveled plain, upon which the 
Cambrian sediments rest. 
The Cambrian rocks described continue uninterruptedly south- 
ward from the Grand Wash Cliffs, the basal sandstone being about 
100 feet and the shale about 225 feet thick at the southern end of the 
Juniper Mountains. 
The Redwall limestone continues southward as the highest forma- 
tion of the cliffs, and on account of its superior hardness maintains 
the precipitous face. It thins southward, probably owing to erosion, 
until at the southern end of the Juniper Mountains it is only 450 
feet thick. 
The section near Nelson, in Truxton Canyon, yielded the fossils 
previously described, showing that the Redwall limestone is partly 
of Mississippian and partly of Pennsylvanian age. Although exam- 
ined with considerable care, no fossils were found in the limestone 
at the southern end of the Juniper Mountains. 
TRUXTON PLATEAU. 
Location. — Lying between the Yampai Cliffs on the east and the 
Cottonwood and Aquarius cliffs on the west, is a comparatively level 
plain extending from Music Mountain southward to the Aquarius 
Mountains. The writer crossed it in two places near the northern 
end, as shown by the routes of travel delineated on PL I. In the 
vicinity of Truxton Canyon it is locally known as the Truxton Plateau, 
and this name may be used to designate the entire area. 
Topographic features. — The plateau, which lies about 5,000 feet above 
sea level, consists of eroded granite, nearly covered with eruptive 
rock, which fills the depressions, leaving the higher granite points 
exposed above the lava. In other words, the Truxton Plateau is a 
lava-covered peneplain which has been slightly dissected by a few 
streams that have cut narrow canyons. Back from the edge of the 
plateau these are shallow, but they deepen rapidly as they near the 
cliffs to the west, a fact indicative of comparatively recent uplift. 
Bock masses. — The rocks of the plateau are pre-Cambrian granites 
overlain by Tertiary rhyolite and andesite, together with basalt of 
more recent origin. The plateau was not visited south of Trout 
Creek, but, seen from a distance, the igneous rock apparently extends 
continuously southward to the great masses of rhyolite and andesite 
of the Aquarius Mountains. 
