444 University of California Publications in Geology [Vol. 11 



GEOLOGIC RELATIONS OF THE TERTIARY FORMATIONS 



The Tertiary sediments of the Mohave area rest upon a basement 

 including granites and schists of pre-Tertiary age, and extrusive 

 igneous rocks presumably at least as old as Lower Miocene. A flow 

 of basic andesite or of acid basalt overlies the granitic rocks and 

 underlies the basal Tertiary sediments of the Barstow syncline. A 

 rhyolite described by Lindgren from the Calico Mountains is stated 

 by Baker to underlie beds considered to represent the Rosamond 

 Series. 



Excepting marine deposits of Eocene age, the oldest Tertiary 

 rocks in the Mohave area of which the age is certainly known are 

 included in the Barstow formation representing the upper Miocene. 

 The Barstow fauna is found in the uppermost or Fossiliferous Tuff 

 member of the five divisions referred by C. L. Baker to the Rosamond 

 Series in the section north of Barstow. The Resistant Breccia mem- 

 ber immediately below the Fossiliferous Tuff member of Baker's 

 section also contains mammalian remains presumably of the same 

 faunal stage as those of the member immediately above. The only 

 known fossil remains occurring below the Resistant Breccia member 

 in the Barstow syncline section consist of a single imperfectly pre- 

 served fresh-water gastropod found in the third member from the 

 upper end of the section. This specimen does not furnish definite 

 evidence of age of the beds in which it occurs. 



Leaves stated by F. H. Knowlton to resemble Eocene species were 

 collected by H. W. Fairbanks 17 near the base of the Ricarclo section 

 at Black Mountain near El Paso Range on the western border of the 

 Mohave area. There is some doubt as to the age of these specimens, 

 as also regarding their occurrence, and recent examination of the 

 old coal workings from which the plants were obtained has not fur- 

 nished sufficient information to permit a judgment as to the age of 

 the plant-bearing beds. 



Dr. Fairbanks reported the occurrence of a seam of coal fourteen 

 inches thick, enclosed between clay strata, and apparently occupy- 

 ing a position below the tuffs to the southeast of Black Mountain. 

 Impressions of leaves in the clay above the coal were examined by 

 Dr. Knowlton who reported that they represent three small fragments 

 of plants belonging in two species, Sapindus affinis Newb. and Anemia 

 subcretaoea (Sap.) Ett. and Bard. This material was considered as 



it Amer. Geol., vol. 17, pp. 63-74, 1893. 



