388 University of California Publications in Geology I Vol. 9 



During a recent visit to the Marysville Buttes the writer obtained 

 evidence that the lone as mapped in the Marysville Folio 41 consists 

 of Chieo Cretaceous, Tejon Eocene, and a formation made up of 

 rhyolitic tuff, conglomerates, and thin flows of igneous rock evidently 

 derived from vents which are now represented by volcanic necks 

 designated on the map as "Nr." This last formation rests with 

 marked unconformity upon the two older terranes mentioned and is 

 in turn unconformably overlain by andesitic flows of a later period. 



THE EOCENE OF OROVILLE SOUTH TABLE MOUNTAIN 

 Location 



In a recent paper entitled "The Fauna of the Eocene at Marys- 

 ville Buttes," the writer 42 recognized a new faunal zone in the Tejon 

 group of California and identified the supposed marine lone of the 

 Marysville Buttes as Tejon Eocene. The study of the sediments be- 

 neath the Older Basalt has resulted in the recognition of these sedi- 

 ments as Tejon Eocene of the same age as the uppermost Eocene 

 of the Marysville Buttes, the Siphonalia sutterensis zone. These 

 sediments are littoral deposits, the inshore equivalents of the sedi- 

 ments deposited in the deeper waters of the Marysville Buttes region 

 during Eocene time. 



The Eocene strata outcrop near the town of Oroville on the 

 west side of the Sacramento Valley. These strata have been previ- 

 ously regarded as Miocene and were mapped as the lone Forma- 

 tion by Lindgren. The principal fossil localities are located about 

 two and one-half miles north of the town on the south side of Oro- 

 ville South Table Mountain, a flat-topped hill, 1050 feet in eleva- 

 tion. (See Plate 43, Figs. 1 and 2.) The beds in which the fossils 

 are found are nearly horizontal. In some places they have a dip 

 of about one degree to the southwest. They rest upon rocks of 

 Chico age and upon the bedrock complex of the Sierra Nevada, and 

 are capped by a basaltic lava flow which varies in thickness from 

 fifty to two hundred feet. Oroville Table Mountain and the South 

 Mountain, with other and smaller flat-topped hills in the vicinity, 

 are remnants of an extensive flow which, according to Turner, came 

 from a point about twenty or thirty miles to the east. The name 

 Older Basalt was given to this lava on the geological map of the 



« Lindgren, W., and Turner, H. W., Marysville Folio, U. S. Geological 

 Survey, Folio 17, 1895. 



42 Dickerson, Roy E., The Fauna of the Eocene at Marysville Buttes, Cali- 

 fornia, Univ. Calif. Publ. Bull. Dept. Geol., vol. 8, pp. 257-298, 1913. 



