50 REPORT OF THE CALIFORNIA EARTHQUAKE COMMISSION. 
practically straight, with a bearing of N. 37° W., for 35 miles; but there are slight curva- 
tures in the fault-trace within the Rift. For example, the fault-trace, in its path thru 
Tomales Bay, must be slightly convex to the southwest to clear the little headlands on 
the northeast side of the bay, as it apparently does. There is a similar slight con- 
vexity to the southwest between the head of Tomales Bay and Bolinas Bay. The com- 
plementary concavity between these two convexities is near the head of Tomales Bay. 
Between Mussel Rock and San Andreas dam, the fault-trace has a slight concavity 
to the southwest. The projection of its course seaward from Mussel Rock would 
not meet the southward projection of the fault-trace from Bolinas. There can be little 
question as to the continuity of the fault-trace across the Gulf of the Farallones; and its 
path on the bottom of the Gulf must, therefore, take the form of a very flat sigmoid curve, 
with a slight concavity to the southwest in the Bolinas moiety of the submarine segment 
and a corresponding convexity at the Mussel Rock end. Between San Andreas dam and 
Chittenden, the fault-trace indicates a pronounced curvature in the general trend of the 
Rift. The chord between these two points is about 55 miles in length and bears N. 44° 
W. The fault-trace lies wholly to the southwest of this line, with convexity toward the 
Pacific. The point on the curve most distant from the chord is about its middle part, 
the distance being about 2.25 miles. On this segment of the Rift there is locally a rather 
abrupt reversal of the curve, south of Black Mountain, which is best seen on map No. 22. 
Between Chittenden and a point near Priest Valley there is another pronounced curva- 
ture in the general course of the Rift, where it passes over to the northeast flank of the 
Gavilan Range. Here the curvature is concave toward the southwest. The chord is 
60 miles long, and bears, as before, N. 44° W., and the Rift lies wholly on the northeast 
side. The point on it most distant from the chord is near the middle of the segment, 
and the distance is 2.4 miles. From Priest Valley to the south end of Carissa Plain, the Rift 
is nearly straight, but with minor curvatures which can not be more particularly defined, 
owing to the absence of good maps. The general bearing for this segment is about 
N. 40° W. 
The marked curvature between the south end of Carissa Plain and Tejon Pass has 
already been noted. From the latter place to the north end of the Colorado Desert, beyond 
which the Rift has not been traced, there are numerous curvatures in the course of the 
Rift; but since the Rift for this segment is indicated on maps Nos. 6 to 15 on a scale of 
1 or 2 miles to the inch, it will be unnecessary to do more than refer to these maps for 
their characterization. The general course of the Rift in this region is a flat curve con- 
cave to the south-southwest. 
It thus appears that the Rift, as a whole, has a curved course convex to the Pacific; 
and that this general curvature is characterized by a succession of slightly curved, rather 
than straight, segments. The amount of the curvature, as it appears upon the maps, is 
determined to some slight extent by the character of the projection. But the general 
conclusion above reached without quantitative expression is independent of the projection 
adopted for the maps. 
A most interesting general feature of the Rift is in relation to the granitic rocks of the 
Coast Ranges. The granites of the southern Sierra Nevada pass into the Coast Ranges 
in the vicinity of Tejon Pass, and extend thence in a series of more or less elongated but 
discrete areas thru the Santa Lucia, Gavilan, and Santa Cruz Ranges, and beyond the 
Golden Gate to Point Reyes Peninsula and Bodega Head. From the southern end of 
Carissa Plain to Bodega Head, this granite lies wholly to the southwest of the Rift. 
At one point in the Rift, however, in Nelson Canyon, Fairbanks has found the granite 
exposed on the northeast side of an old fault having a downthrow on the southwest. 
Southward it passes into a region where granitic rocks prevail on both sides of the Rift. 
The Rift in the Coast Ranges thus appears to serve as a line of demarkation between two 
