52 



SCIENCE 



[N. S. Vol. XLI. No. 1045 



in the Redding quadrangle, but, more or 

 less distinctly marked, it extends through- 

 out the great stretch of the Paleozoic rocks 

 •of the whole group in both California and 

 Oregon. Furthermore, the same curved 

 trend is suggested by the form of the in- 

 truded masses. The mass of granodiorite 

 tetween Lewiston and Igo extends south- 

 east and widens directly toward the Sierra 

 Nevada, where similar rocks are abundant. 



While the composition and the plication 

 of the rocks of the Klamath Mountains tend 

 to show close relationship to the Sierra 

 Nevada, it is only partial, and in reality the 

 two are distinct, being separated in the 

 first place by a wide depression probably 

 due, as long ago pointed out by Whitney, 

 to a fault across the trend of the range, and 

 in the second place characterized by a series 

 of overthrust faults quite unlike those which 

 ^obtain in the Sierra Nevada. 



-Although the detailed structure of the 

 Klamath Mountains has not been worked 

 out, some of the major structures have been 

 apprehended by Hershey and others suffi- 

 ciently for consideration in this compari- 

 s6n of the several ranges of the Pacific 

 coast chain. 



The southwest limit of the Klamath 

 Mountains against the coast range of Cali- 

 fornia is marked by a profound thrust 

 fault on which the highly crystalline schists 

 of South Fork Mountain appear to have 

 been thrust to the southwest up over the 

 Cretaceous and Jurassic rocks toward the 

 coast. The fault runs northwest and south- 

 east and the hard schists give rise to a 

 prominent long even-crested mountain 

 ridge, one of the most conspicuous mem- 

 bers of the Klamath Mountain group. 



In Oregon a similar fault occurs through 

 the Kerby region of Josephine County, 

 where Devonian rocks are in effect thrust 

 northwest toward the ocean up over those 

 of Jurassic age. The fault runs northeast 



and southwest and erosion has developed 

 prominent mountains facing the valley 

 that lies to the northwest. 



The Kerby fault if continued southwest 

 in the same strike would intersect the South 

 Fork Mountain fault, but, according to 

 Hershey, before it reaches the South Fork 

 Mountain fault it curves to the south and 

 finally southeast so as to parallel the South 

 Fork Mountain fault. 



Farther east there is another fault belt 

 which at the south end in California trends 

 southeast, while at the northern end in Or- 

 egon its course is to the northeast. Like 

 the other, it appears to be a thrust fault. 

 Hershey has estimated the overthrust 

 locally in one of the Klamath Mountain 

 faults as much as a mile. 



The curved thrust faults traversing the 

 Klamath Mountains are in strong contrast 

 with the normal faults of the Sierra 

 Nevada. The Klamath Mountain thrust is 

 to the westward. The downthrow of the 

 normal faults in the Sierra Nevada is to 

 the eastward. Thrust faulting occurs also 

 locally in the Sierra Nevada, but at Tay- 

 lorsville the thrust is to the eastward. 



The Klamath Mountains are insular in 

 character. Composed largely of Paleozoic 

 rocks and surrounded by rocks of later age, 

 they formed a buttress in the development 

 of the coast ranges of California and Or- 

 egon. From the Sierra Nevada they are 

 separated by a depression in the older rocks 

 that extends northward beneath the Cas- 

 cade range. 



During a portion of the Cretaceous the 

 Klamath Mountains were above sea level, 

 but the gradual subsidence of the land al- 

 most or quite completely immersed them 

 at the close of the Chico epoch, as shown 

 by the rather widespread occurrence of 

 fossiliferous fragments of sandstone from 

 the Chico formation in the auriferous grav- 

 els of that region. During the early Ter- 



