40 REPORT OF THE CALIFORNIA EARTHQUAKE COMMISSION, 
The depression is probably associated in some manner with one of the movements along 
the Rift. Upon the eastern edge of the valley there is an escarpment about 100 feet 
high, due to an upward movement upon the northeast side of the Rift. 
Southeast of Bitterwater, the Rift leaves the younger formation, and at Lewis Creek 
both walls are in the Franciscan rocks. For 20 or 25 miles now, the peculiar features 
of the Rift by which we have followed it are almost absent. The Franciscan series, 
including old sedimentary rocks, serpentines, and other basic igneous rocks, does not 
lend itself well to the preservation of such records, but appears to be greatly broken and 
crusht and marked by enormous landslides in the vicinity of the Rift. The Rift crosses 
Lewis Creek about 2 miles above its mouth and then passes up over a high ridge lying 
between Lewis Creek and San Lorenzo Creek. On the north side of Lewis Creek there is 
an enormous landslide, which has nearly blocked the valley. The slide is undoubtedly 
hundreds of years old. The ridge on to which the Rift passes after leaving Lewis Creek 
is crost by it at such a small angle that it does not reach the southern base until we get 
to the head of Peach Tree Valley, a distance of 20 miles. The ridge its whole length is 
shattered and broken, and, as before said, marked by innumerable rockslides. The rather 
steep slopes appear to move every wet season. ‘The headwaters of the San Lorenzo 
Creek (Peach Tree Valley) have been robbed by Gaviota Creek, possibly as a result 
of some movement connected with the Rift. Just above where the stream has been 
diverted, there is another great landslide which the road crosses to reach Slack Canyon. 
At the mouth of Slack Canyon, the Rift leaves the Franciscan series, and coincides 
again with an ancient fault in which the Miocene sandstones are thrown down upon the 
southwest against the older formation just referred to. Passing from Slack Canyon over a 
divide, we come to the headwaters of Indian Creek and Nelson Canyon. As the Rift oc- 
cupies steep slopes much of this distance, it is distinguished chiefly by landslides and rapid 
gullying of the surface. In Nelson Canyon the Rift follows an old fault in which the Mio- 
cene formation has been thrown down upon the southwest side, and the northeast wall so 
raised that the granite on which the Franciscan series rests is exposed. Ascending the 
divide toward the head of Nelson Canyon, a long, nearly straight ridge of Miocene clays 
divides the drainage and appears to be due to some one of the movements along the Rift. 
The Rift can be traced thru the hills at the head of the Cholame Valley by its character- 
istic features, as well as by bluffs which are undergoing rapid erosion. It crosses the road 
a mile west of Parkfield and exhibits here a regularly rounded ridge 200 feet wide and 
20 feet high at the most elevated point. (Plate 198.) That the ridge must be hundreds 
of years old is shown by the great oak trees that are growing upon it. One white oak is 
fully 8 feet thru. Large springs mark the fissure at this point, and are found along it the 
whole length of the Cholame Valley. According to a resident, the Rift opened along the 
ridge in the earthquake of 1901, the opening being distinctly traceable for several miles. 
Southeasterly from the point Just described thru the Cholame Valley, there appears no 
very prominent ridge or escarpment, altho springs and cienegas, marking a gentle swell 
in the flat open surface of the valley, indicate the line of the Rift. 
The region about Parkfield, in the upper Cholame Valley, has been subjected to more 
frequent and violent disturbances than almost any other portion of the entire Rift. An 
auxiliary fissure begins near the main Rift a little west of Parkfield, and extends in a 
more easterly direction along the east side of Cholame Creek. (See plate 20.) The once 
flat, open valley has been broken along this line, and a bluff nearly 200 feet high formed 
facing the Creek. This bluff, now deeply eroded, must have been formed during one of 
the oldest disturbances. The lowland between this bluff and Cholame Creek shows the 
effect of great disturbance over a considerable area. Innumerable hollows interlace and 
extend in all directions. They resemble nearly obliterated creek beds except that they 
have no outlets. Parallel with the front of the dissected bluff, but a little back from 
