1921] Frich: Faunas of Bautista Creek and San Timoico Cafion 285 



HISTOEY OF THE EEGIONS 



California during Pliocene time was very much as today. The 

 land was gradually rising, and on the submerged narrow coastal plain 

 was laid down a great thickness of marine beds.** Fortunately for 

 the record of life forms of the time this elevation was not uniform, 

 and through local subsidence older Miocene valleys in the Coast 

 Ranges, sections of the Great Valley, and basins such as that then 

 existing in the region northwest of San Jacinto were filled with land 

 laid sediments." 



In the neighborhood of Eden these Pliocene sediments covered the 

 earlier and coarser deposits, such as now seen along Potrero Creek, and 

 buried to a depth of many feet any rough island-like bosses of the 

 older rock that rose above the uneven basin floor, like the present Eden 

 monadnoek. The materials of the deposition were fine surface sands 

 and muds derived from the erosion of the granitic and metamorphic 

 rocks of a near-by highland terrane. They were of unassorted finer 

 grades of alluvial material, that point to a development under arid 

 conditions where disintegration was in advance of weathering.^" They 

 were doubtless spread out as silt over what was then a region of shallow 

 brackish lakes and plains. 



It was an interesting assemblage that then roamed the Eden wilds. 

 Grazing over the open stretches were great droves of fleet, light-limbed 

 horses, half a dozen or more species of camels, bands of large and of 

 small antelope, and herds of deer. Within the edge of the scrub 

 might have been seen pigs and larger boar, or an occasional herd of 

 curious, four-tusked proboscideans. In the forests lived sabre-toothed 

 cats, ground-sloths, wolves, and huge bears larger than the largest 

 Kadiak of today. 



In richness and variety this extinct American fauna must have 

 compared well with the existing African, the bovid antelopes in their 

 multiplicity of form and the herds of zebra of present Africa recalling 



8 Smith, J. P. Geological History of California. Science, n.s., vol. 30, p. 346, 

 1909. 



■ 9 The length of the Cenozoie Era, the Age of Mammals, has been placed, 

 through computations based on the total thickness of sedimentary rocks compared 

 with present ratios of accumulation, at about three million years (Dana, 1874, 

 Walcott, 1893). The last sixth of this period, or 500,000 years, is accepted as the 

 length of the Quaternary (see Osborn, "The Age of Mammals" and "Men of 

 the Old Stone Age"). According to the same reasoning the duration of the 

 Pliocene would have been from 750,000 to 1,000,000 years, which would place 

 Eden age, late Lower Pliocene, in the neighborhood of 1,000,000 B.C. 



10 The analysis of rock specimens was very kindly carried out for the writer 

 by Professor G. D. Louderbaek. 



