76 University of California Publications in Geology [Vol. 10 



provinces, the writer examined an area of sedimentary deposits near 

 Tehachapi Pass, in the southern Sierra Nevada. This area lies directly 

 between the San Joaquin Valley and the Mojave Desert. Because of 

 its position it seemed probable that its study would yield critical infor- 

 mation bearing upon the question of correlation between the two 

 provinces. Reconnaissance examinations by the writer in the winter 

 of 1912 and in the summer of 1914 had, moreover, suggested the proba- 

 bility of the presence of mammalian fossils in the exposures of sedi- 

 mentary strata in the Tehachapi area. 



As the result of several weeks' work in the Tehachapi Pass region 

 in November and December, 1914, two fossil faunas were secured at 

 quite widely separated horizons. More material was obtained in June, 

 1915, in the collection of which the writer was ably assisted by Clarence 

 L. Moody, James M. Douglas, and Edward Thacher. 



Though the collections are not large, they are thought to contribute 

 new information relating to the history of the Mammalia of western 

 North America, and bearing on the geologic history of the southern 

 Sierra Nevada and adjacent regions. 



This paper is a summary statement of the composition and rela- 

 tionships of these faunas. Detailed descriptions of the faunas and a 

 discussion of the geologic results are to follow. 



Occurrence 



The Tertiary formations in which the mammalian faunas are found 

 in the Tehachapi region are in part an extension of beds first brought 

 to notice by Professor Andrew C. Lawson, 1 who described strata ex- 

 posed in the vicinity of Monolith and lower Cache Creek, near Teha- 

 chapi Pass. 



The formations are included in a section of volcanic and terrestrial 

 materials extending over an area of seventy-five to eighty square miles 

 or more of the summit region of the southern Sierra northeast of the 

 town of Tehachapi. The total thickness of the formations is probably 

 not less than four or five thousand feet. Constituting the group are 

 basic lava flows, volcanic agglomerates, massive pumiceous tuffs, strati- 

 fied ash beds, terrestrial sandstones, clays, cherts, and fanglomerates. 

 The fossiliferous horizons are probably stratigraphically near the 

 middle of the section. The whole succession of strata records recur- 

 rent volcanic activity, with intervening periods of subaerial and lacus- 

 tral deposition. The angular fanglomeratic character of the coarser 



i Univ. Calif. Publ., Bull. Dept. Geol., vol. 4, pp. 431-462, 1906. 



