44 REPORT OF THE CALIFORNIA EARTHQUAKE COMMISSION. 
An extended study would be necessary to determine in detail the geology of the Rift 
from Gorman Station eastward. Near Gorman a dike of basaltic or andesitic lava extends 
parallel with it for some distance. Granitic rocks often form one side, while soft Tertiary 
beds of a light or reddish color frequently appear in the raised ridges. Between Palm- 
dale and Big Rock Creek, low discontinuous ridges, springs, and cienegas point out the 
line of the Rift, altho there are stretches of several miles at a time where either the 
original displacement was not great or erosion has removed its effects. Four miles 
west of Big Rock Creek there is one fine escarpment 0.333 mile long and 40 feet high, 
facing the mountains on the south. (Plate 27a.) In this section there are indications 
of at least two movements. (See plate 268.) The Rift passes just below Big Rock P.O. 
east of Big Rock; a trail on the northern slope of the mountains and a wagon road on 
the southern side of the divide follow the Rift continuously to a point near the mouth of 
Cajon Canyon. On the north side of the mountains (San Gabriel Range) there is no im- 
portant depression on the Rift between Big Rock Creek and Swartout Valley; never- 
theless the comparatively recent movements have been of sufficient magnitude to produce 
ridges and hollows giving a continuous and easy route for the trail along the slope of the 
mountains. 
Before reaching the divide leading over to Swartout Valley, we encounter some striking 
features. Near the head of Mescal Canyon a ridge has been split away from the mountain, 
diverting the little streams from above and making two drainages where one would 
normally appear. In places this ridge (plate 278) is as sharp and as perfect as tho formed 
but yesterday; but the great pine trees, growing upon its top and sides (the altitude here 
being nearly 7,000 feet), tell us that it must be hundreds of years old. At the head of 
the canyon the trail leads thru a sharp V-shaped cut where the bare sliding surfaces 
make it appear as if movement had recently taken place in the Rift. (See plate 28a.) 
Passing over a sag in the mountains to Swartout Valley, the Rift is less prominent 
as a topographic feature, but a line of springs marks its course. Lone Pine Canyon 
is remarkable for its length and straightness. The Rift passes down its whole 
length but it is not very prominent. Springs appear at several points, also small 
cienegas with a slight escarpment below them. At the mouth of Lone Pine Canyon and 
a little above its junction with the Cajon Canyon (plate 28x) are more interesting features. 
Two lines of displacement appear here, and between them a long, narrow sunken block 
with a small lake in its lowest portion. (See plate 29a.) 
The line of disturbance now crosses Cajon Canyon, giving rise to broken and sliding 
cliffs; and then, passing over a spur of the San Bernardino Range, comes out at its foot 
before reaching Cable Canyon. From this point the Rift continues on southeasterly at 
or near the junction of the gravel slopes of the San Bernardino Valley and the steep moun- 
tain slopes of crystalline rocks. The uniformly straight course which the Rift exhibits in 
this portion of its length takes it diagonally across the mountains from the northern and 
desert side of the San Gabriel Range to the southern side of the San Bernardino Range. 
The torrential streams emerging from the San Bernardino Range upon the gravel slopes 
of the broad valley at its base have cut wide flood plains in the ancient gravels which 
accumulated along the foot of the mountains. The remaining portions of this old slope 
lying between the stream plains are called mesas. Back of Devore Heights there appears 
a rounded ridge formed out of the mesa gravels. As we continue toward Cable Creek, 
springs and cienegas are found to be numerous just above it. East of Cable Creek the 
ridge becomes an escarpment facing the valley, and in places shows a height of about 75 
feet. Viewed in profile, this escarpment breaks the uniform slope of the mesa gravels, 
almost reversing their slope on the upper side. On the west side of Devil Canyon there 
is a double escarpment in the gravels, both apparently being due to movements along the 
Rift. (See plate 298.) Back of the Muscupiabe Indian reservation and north of the 
