402 Diller — Mesozoic Sediments of Southwestern Oregon. 



The Mesozoic Sediments of Southwest Oregon. 



Introduction. 



The Klamath Mountains of southwest Oregon and the adja- 

 cent portion of California, like the Sierra Nevada, are com- 

 posed in large part of Paleozoic sediments associated with 

 masses of intrusive and effusive rocks of various ages. Meso- 

 zoic sediments are of less amount than the Paleozoic and have 

 their most extensive development along the mountain borders, 

 from which they overlap and by deformation are so involved 

 with the older rocks as to form an important structural ele- 

 ment of the Klamath mountain mass. 



The peripheral portion of the Klamath Mountains has been 

 surveyed in the Lassen Peak and Redding quadrangles of Cali- 

 fornia and the Roseburg, Coos Bay and Port Orford quad- 

 rangles of Oregon. The remaining peripheral portion, as well 

 as the mountains themselves, has been covered by reconnais- 

 sance, and the general results in areal distribution are shown 

 upon the geological map of North America, published by the 

 International Geological Congress for the meeting in Mexico, 

 1906. 



The study of the Mesozoic in southwest Oregon is far from 

 complete, but the publication of the map referred to above and 

 the general interest in the region, as shown by Mr. Louder- 

 back's article in the Journal of Geology for September, 1905, 

 p. 511, call for additional data, which this paper is intended to 

 partly supply. It will, however, be limited to the consider- 

 ation of the sedimentary rocks only, since they alone contain 

 the records of geologic age to which the others must be 

 referred. 



Subdivisions Discriminated. 



The Mesozoic, as far as known in southwest Oregon, belongs 

 to the Cretaceous and Late Jurassic. The bottom of the latter 

 has not yet been determined, and what may lie between it and 

 the Paleozoic rocks of the same region is a matter for further 

 investigation. The bodies of strata thus far discriminated are 

 as follows: 



Cretaceous 



Chico formation 

 Myrtle " 



Jurassic 



Dothan formation 

 Galice " 



