SOUTHERN PACIFIC LINES 275 
schists, and crystalline limestones, all metamorphosed sedimentary 
deposits, penetrated by granitic and other igneous rocks. Their 
length is about 5 miles, and they are surrounded by valley lands. 
Beyond the west end of this range is the north end of the high Santa 
Ana Mountains,*! which extend southeast from Corona. 
From Bloomington to Ontario there are several settlements occu- 
pied with the extensive culture of grapes, lemons, peaches, and other 
fruits. In this region the San Bernardino Plain is 
more than 20 miles wide, extending from the foot of 
the San Gabriel Mountains to the Santa Ana River 
ge Sa Orleans 1,959 which flows near its southern margin. It is bordered 
on the west by the San Jose and Puente Hills, which 
make a barrier trending north-northwest, beyond Pomona. To the 
north near Guasti are fine views of Cucamonga Peak (elevation 8,911 
feet), one of the high summits of the southern ridge of the San Gabriel 
Mountains, and the still higher San Antonio Peak (elevation 10,080 
feet) is farther back on the northern sky line. Deep canyons lead 
out of these mountains at short intervals, and most of them contain 
streams whose water, if not diverted by irrigation ditches, sinks at 
the mouths of the canyons and passes as a general underflow into the 
gravel and sand of the slope beyond. In times of freshet the streams 
flow greater or less distances across the slope, carrying much sedi- 
ment, which is dropped as the water spreads out on the plain. Occa- 
sional great floods cross the plain, but much of the large volume of 
water they carry at such times is absorbed by the porous gravel of 
the stream beds. The courses of these ephemeral streams across the 
plain are marked by dry washes, usually shallow sandy channels, 
many of them splitting up irregularly and some of the branches 
rejoining. One effective method of conserving water in this region, 
where it is so valuable, is to divert flood waters near the canyon 
mouth, causing them to spread out widely over the coarse deposits, 
where they sink, thus adding to the volume of underflow tapped by 
many wells. 
by great igneous intrusions and com- | basic lavas and tuffs, and all are cut 
pression. It is believed that the range | and altered greatly by masses of 
was uplifted in greater part in late andesite, granodiorite, and diorite 
Tertiary time. Apparently the uplift | which have been intruded in a molten 
consisted of the rise of a huge block of | condition. Next above there is a west- 
the earth’s crust along fault lines | ward-dipping succession of Upper Cre- 
mostly trending N. 60° W. The main | taceous and ‘Tertiary strata. In 
block is traversed by minor faults | general, the mountains consist of a 
vhich make complex. | tilted fault block with Soond flexures. 
1 In the Santa Ana Movuitaing the There has been a | es of repeated 
Idest rocks are i 
Guasti. 
nae a ant 
They 
are overlain eerie giz by a| factor. Some of the lower terraces are 
_ Coarse conglomerate and in places by | marine, (B, N. Moore.) 
