36 REPORT OF THE CALIFORNIA EARTHQUAKE COMMISSION. 
by San Mateo Creek which flows in a sharp gorge thru the wider part of the broad, flat- 
topt ridge which separates the valley from the Bay of San Francisco. This stream is 
regarded as a relic of the original consequent drainage of the northeast slope of Montara 
Mountain, which became superimposed upon the Franciscan terrane by the denudation 
of the overlying soft and little coherent Merced formations. From this consequent 
trunk the valley in which San Andreas and Crystal Springs Lakes now lie was evolved 
by subsequent erosion along the line of the Rift, its present features dating from a period 
in the Pleistocene later than the removal of the Merced formations. A small portion 
of the upper end of the valley has been captured by the headwater erosion of San Bruno 
Creek. 
To the southeast of Crystal Springs Lake, the valley followed thus far bifurcates about 
2 miles beyond the lake, on either side of a median ridge. The two branches are nearly 
parallel. The east branch rises to a wide and rather flat divide, with streams heading 
in it from both sides. The other branch, altho it is more incisive, has no well-defined 
stream, but has a small swamp at its lower end. It rises to a sharper divide, from which 
there is a descent into the narrow straight canyon of West Union Creek. It is this 
western depression that the Rift follows. Near Woodside the canyon of West Union 
Creek expands into a more open valley, with steep mountains on the southwest and 
lower hills on the northeast. The Rift follows this straight valley (plate 168) to its 
southeastern end, and then ascends to the saddle which separates Black Mountain from 
the mountains to the west. From this saddle it descends to the narrow canyon of 
Stevens Creek. It crosses the canyon at a small angle near its upper end and parallels 
the creek on the southwestern side, at an elevation of about 500 feet above it. It then 
passes thru the saddle between Stevens Creek Canyon and Congress Springs, and keeps 
well up on’ the slopes to the west of Congress Springs behind a series of shoulders and 
knolls to a reservoir on a saddle thru which it passes. From this saddle southeastward 
the line of the Rift again lies along the southwest side of a longitudinal valley and so 
continues on a line independent of the present drainage to the pronounced notch in the 
crest line of the range at Wright Station. 
In this stretch of the Rift from Crystal Springs to Wright, the coincidence of the Rift 
with the major geomorphic features is very striking for the first half of the distance. 
In the second half, if we judge by the fault-trace, it appears to be quite independent of, 
tho parallel to, the canyons; and its only manifest relationship to the geomorphic fea- 
tures is its coimcidence with a series of saddles or windgaps in the transverse spurs of 
the mountains. Its general parallelism with, and proximity to, the crest of the range 
thruout the entire stretch is pronounced. In the notch at Wright, the Rift intersects 
the crest line and passes from the northeastern flank of the range to the southwestern. 
The general features of the Rift from Wright to Chittenden are described by Mr. E. 8. 
Larsen in the following note: 
From the hills above Wright Station to the village of Burrell, a distance of about 
_ 2 miles, the Rift follows along the ridge above Los Gatos Creek, which drains to the 
east. The drainage of the western slope of the ridge is to the Pacific. For most of this 
distance the Rift is a short distance on the Los Gatos Creek side. It usually occupies a 
small, trough-like depression; or, where it cuts just above the heads of the small gullies, 
there are low, rounded knolls between the gullies. These knolls are seldom over 30 
feet higher than the trough. Just southeast of Burrell, the Rift traverses the ridge and 
follows a gully into Burrell Creek, which it crosses. It continues in a southeasterly 
direction, parallel to the creek and about halfway up the ridge to the southwest of it. 
The elevation of the ridge is only about 400 or 500 feet above the creek bed, and the top 
is rounded, with a steep slope below this to the Rift, and a gentle slope below the Rift 

