BLOCK FAULTING IN THE KLAMATH LAKES REGION 235 
east wall of the graben. This is the western face of what may be 
called the Modoc Point block mountain, which stands in the same 
relation to the graben as the Fort Klamath block farther north, 
and, like the latter, has a more gentle eastern back slope. The 
west-facing fault scarp is remarkable for its youthful appearance, 
erosion having modified it but slightly, and for the straightness 
of its base line for many miles at a stretch. At Modoc Point itself 
the strike of the fault changes rather abruptly from N.-S. to S. 35 E- 
Fic. 5.—Slickenside surface exposed along road cut in north end of Plum Ridge. 
(Photo by J. P. Buwalda.) 
On the face of the range farther south is a prominent “fault-block 
splinter,” clearly shown in Fig. 4, from a photograph of Modoc 
Point looking northward from the northern end of Plum Ridge. 
The same view illustrates the youthful character of the fault scarps. 
It must not be supposed that the back slopes of the Fort 
Klamath and Modoc Point blocks are as smooth and featureless 
as their fault faces. Both blocks are remarkably youthful in the 
present cycle of erosion, as the descriptions of their fault scarps 
fully indicate; but no description would be complete which did 
not include an account of the stage of erosion reached in the pre- 
faulting cycle, as indicated by the topographic aspect of the back 
slopes. Our route of travel gave little opportunity for observation 
