34 REPORT OF THE CALIFORNIA EARTHQUAKE COMMISSION. 
is responsible for some of the western ridges of the Rift belt; but with that exception, 
the ridges and sags of the Rift are occasioned by the unequal settling of small crust 
blocks along a magnified shear zone. (Fig. 8.) 
The limits of the Rift are not definite. The boundaries drawn in fig. 2 serve to 
indicate the belt in which the Rift structure dominates the topography, but do not 
indicate the limits of the Rift structure. Within the belt the dislocations have been so re- 
me ee | 
Se 
La 
Fic. 9. — Cross-profiles of the Rift arranged in geographical order with the most northerly at 
top and northeast ends at the right. Positions of fault-trace and its branches are indi- 
cated. The profiles are copied from field sketches made without measurement. 
cent and of such amount as to keep ahead of weathering and erosion, so that their expres- 
sion has been little dimmed by the processes of aqueous sculpture. Outside the belt the 
evidences of recent dislocation are less striking, but nevertheless exist. The inter-stream 
ridges of the northeastern slope are here and there indented and creased in such a way as 
to indicate recent faults of small amount trending parallel to the Rift. In the vicinity 
oa _— 
