THE SAN ANDREAS RIFT AS A GEOMORPHIC FEATURE. 27 
of the features of the Rift for this part of its course, we are chiefly indebted to the 
observations of F. E. Matthes and H. W. Fairbanks. For this stretch its course is some- 
what more meridional than the trend of the coast, so that it converges steadily south- 
ward upon the shore line, and finally intersects it below Fort Ross. Between the mouth 
of Alder Creek and the Garcia River the Rift is marked across a low, rolling country by 
a series of depressions, swamps, and ponds, many of which are without outlet. At the 
point where it intersects the Garcia River, the valley of the latter from that point up- 
stream for a distance of 9 miles follows the Rift (plate 3c, p), and its course has with 
little question been determined by the structural conditions inherent in the Rift. On 
the southwest side of the valley the minor features of low ridges and swamps are com- 
mon, and there are in places two sets of parallel ridges. From the head of the longi- 
tudinal valley of the Garcia, the Rift passes over a sag in the mountains to the Little 
North Fork, of the Gualala River. From this point southeast, the Rift follows the 
common and very straight valley of the Little North Fork and the South Fork of the 
Gualala. This valley is separated from the coast by a ridge varying in height from 
300 to about 1,000 feet. The Rift follows the valley, or rather the valley follows the 
Rift, for a distance of about 18 miles, and is characterized by the usual abnormal features 
of low ridges, with elongated swamps and ponds between, extended parallel to the river. 
The ridges again evince a tendency to appear in pairs, which is peculiarly marked near 
Stewarts. North of Plantation House the Rift passes over a broad, swampy divide in 
the coastal ridge (plate 2B), and at the House is marked by two small ponds. South 
of the Plantation House is a series of swampy hollows extending toward Buttermore’s 
ranch. The latter lies in a broad, swampy saddle. From Buttermore’s ranch south- 
eastward the Rift is marked by a line of deformation traversing the uplifted wave-cut 
terraces and sea-cliffs which are notable features of this part of the coast. Low ridges 
with northeasterly scarps form barriers which pond the surface waters and give rise to 
numerous ponds and small swamps or elongated hollows. Several small ravines and 
gulches lie in its course, and occasionally a landslide is clearly related to the path of 
the Rift. In the vicinity of Fort Ross, the geomorphic forms of the Rift are particularly 
well exemplified and a typical stretch of the latter is cartographically represented on 
map No. 3. Low ridges up to 10 feet in height, some with mature rounded slopes, 
others with abrupt slopes to the northeast, mark its course. Alined with these are 
scarps which, by reason of their monoclinal slopes, can scarcely be called ridges. Behind 
the ridges and scarps are pools and small swamps. Some of the small streams follow 
the Rift and have established notable ravines along its course. (Plates 4 and 5.) 
With regard to the geology of the territory traversed by the Rift from the vicinity of 
Point Arena to Fort Ross, Dr. H. W. Fairbanks has kindly examined the ground and 
supplied the following note: 
Except for a strip of sandstones (Walalla beds) of upper Cretaceous age extending along 
the coast north and south of the mouth of the Gualala River, and a triangular area of 
Monterey shale and sandstone underlying the coastal terraces in the vicinity of Point Arena, 
the rocks of almost the entire mountainous region between the upper Russian River Valley 
and the coast belong to the Franciscan. There seems to be but one fault in this region, and 
that is on the line followed by the Rift. The Walalla beds begin upon the coast a little south 
of Fort Ross and, extending inland, form the ridge between the Gualala River and the ocean. 
The formation thins out against the ridge bounding the Gualala Valley upon the northeast. 
The line of junction is an irregular one, for in places the soft sandstones reach quite to the 
top of the ridge referred to. These beds extend along the coast to the northwest for more 
than 30 miles, finally terminating 7 or 8 miles south of Point Arena, where they are overlain 
by the Monterey sandstones and shales. The Rift does not follow the contact between the 
Walalla and Franciscan formations and the vertical displacement does not appear to have 
been very great, as in only one place was it enough to bring up the underlying Franciscan 
rocks upon one of its walls. The Rift, for something more than a mile after emerging from 
the ocean southeast of Fort Ross, lies in the Franciscan formation, and the latter is greatly 
