18 TOPOGRAPHIC DEVELOPMENT OF KLAMATH MOUNTAINS, [bull. 196. 
As one proceeds southward from Eureka the heights of Bear and 
Mail ridges afford extensive views eastward, disclosing the long, even 
crest of South Fork Mountain, which constitutes the divide between 
Mad River and the South Fork of the Trinity. That remarkable crest 
of ancient schists is one of the best-developed portions of the Klamath 
peneplain, and was crossed at two points in 1889, 1 at an elevation of 
nearly 6,000 feet. Its composition and general features as part of the 
great plain of erosion were then noted. 
To obtain a closer view of the South Fork Mountain country an 
ascent was made from Blocksburg to Lassie Peak (5,875 feet), whose 
platform, at an elevation of 5,600 feet, is evidently in an ancient 
plain of very gentle relief. The peak being but little above the 
general level of the plain, the view of that feature is remarkably 
impressive, and it is evident that if the canyons were filled up by 
returning the material carried away by the streams, thus restoring 
the original condition, the surface would be approximately a plain. 
The even crest of South Fork Mountain is broken near the middle by 
a low, rounded knob known as Picket Peak, beyond which the crest 
rises toward the Yallo Bally Mountains, where traces of the plain 
reach 7,000 feet. 
THE BELLSPRING PENEPLAIN. 
The Mad River divides for long stretches are more regular in their j 
crest lines than those of the country to the southwest traversed by 
Eel River and the Mattole, although there are traces of plains and a 
striking correspondence in elevation in many places throughout the 
whole region. 
The greater regularity of the peneplain on the Mad River divides 
as compared with the peneplain of the region to the southwest, is 
related to the Miocene shore line at the time the Klamath peneplain 
attained its greatest development. The position of the Miocene shore 
line is indicated, approximately, on PL I, and near it the Klamath 
peneplain would be expected to show a more advanced degree of 
degradation than farther inland. 
The northern end of the Coast Range was beneath the sea during the 
Klamath peneplain stage, and was brought to the surface by the 
faulting and tilting of the Miocene sediments bordering the Klamath 
peneplain. 
The consequent degradation in course of time reduced the north 
Coast Range region to a peneplain — the Bellspring peneplain, which is 
practically continuous with the Klamath peneplain — but the hard rocks 1 
were not so completely reduced as in the adjacent portion of the Kla- 
math Mountains, where, without essential change of base-level during 
the tilting of the Miocene, the peneplanation continued through both 
i Fourteenth Ann. Rept. U. S. Geol. Survey, Part II, 1894, p. 408. 
