26 REPORT OF THE CALIFORNIA EARTHQUAKE COMMISSION. 
its investigation, it became known as the ‘“‘rift line.” Since the earthquake it has been 
traced as a geomorphic or physiographic feature from Humboldt County to the Colorado 
Desert, with a possible gap between Shelter Cove and Point Arena, where, if continuous, 
it lies beneath the Pacific. Its continuity has, however, been satisfactorily established 
from Point Arena to Whitewater Canyon, at the northern end of the Colorado Desert, 
a distance of 530 miles. Thruout this entire distance it lies along depressions or at the 
base of steep slopes which are either the direct result of crustal displacement or of stream 
erosion, operating with exceptional facility along lines of displacement. There can be 
no doubt that the displacements have been recurrent thru a considerable part, if not 
the whole of Pleistocene time, and that in parts of its extent, at least, the movements 
have taken place on fault-lines which originated in pre-Miocene time. The later move- 
ments on this line have given rise to minor features which subaerial and stream erosion 
have not yet obliterated, and it is these minor features chiefly which have attracted atten- 
tion to the Rift by reason of their striking contrast with more common geomorphic forms 
due to erosion. These minor features are chiefly low scarps and troughs bounded on 
one or both sides by low, abrupt ridges in which frequently lie ponds or swamps of quite 
small extent. 
A summary account will now be given of this rift line as a geomorphic feature. 
HUMBOLDT COUNTY. 
The most northerly point in California at which geomorphic features directly referable 
to the violent rupture of the earth’s crust have been observed are those noted by Mr. 
F. E. Matthes in the vicinity of Petrolia in Humboldt County. Here south of Petrolia, 
on high bare mountain spurs between Cooskie, Randall, and Spanish Creeks, he reports 
the occurrence of several small ponds and ridges such as have been familiar to those 
engaged in the field study of the earthquake phenomena as characteristic Rift features. 
Similar features are also found at the base of these spurs near the shore. ‘These are in 
line with similar features found by the same observer between Telegraph Hill and Shelter 
Cove, a few miles to the southeast. Here, particularly in Wood Gulch (plate 1), is a 
narrow depression with ponds, ridges, and saddles, which appears to be essentially a 
feature due to deformation and to have determined the course of the drainage. The 
course of the depression is about N. 25° W. In this depression lies the trace of the 
fault upon which movement took place on April 18, 1906. Its course, if followed south- 
ward to the cliffs above Shelter Cove (plates 24, 3A, B), heads out to sea with a trend 
nearly parallel to the coast. Great landslides occur along the coast in proximity to 
this line, and are in part on the Rift. The rocks traversed by the Rift in this part of 
Humboldt County appear to consist wholly of shales, sandstones, and conglomerates 
which are probably of Cretaceous age, altho since the geology of the region has not been 
studied, positive statements in this regard can not be made. The region is high and 
rugged, with a very precipitous descent to the sea, King Peak having an elevation of 
4,090 feet at a distance of about 2 miles from the shore. 
POINT ARENA TO FORT ROSS. 
From Shelter Cove to near Point Arena, the Rift, if continuous, lies beneath the waters 
of the Pacific. The continuity for this stretch is of course open to question, and in another 
place the considerations bearing upon this point will be presented. At the mouth of 
Alder Creek, 4.5 miles northwest from Point Arena, the Rift enters the coast from the sea 
and is thence traceable continuously to a point about 2 miles southeast of Fort Ross, 
a distance of about 43 miles, with a nearly but not quite straight course, being slightly 
curved with the convexity toward the ocean. (See map No. 2.) For our knowledge 
