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University of California Publications in Geology [Vol. 10" 



marine origin. On this rests with apparent conformity 3100 feet of 

 Tulare, which is in large part of fluviatile or lacustrine origin. The 

 lower or Etchegoin division is throughout composed of coarse sand- 

 stones, clays, and numerous beds of conglomerate with a minor pro- 

 portion of tuff, coal, gypsum, and limestone. The lithology, together 

 with the character of the invertebrate fauna and the presence of fossil 

 remains of land mammals, gives evidence of shallow-water or terrestrial 

 conditions throughout the Pliocene in the Coalinga region. In order 

 to have this great thickness of strata deposited at or near shore the 

 basin of deposition must have been sinking concomitantly with the 

 rising of the eroded area. That this was not continuous but possibly 

 oscillatory is indicated by the recurrence of important conglomerates 

 at various horizons. A few miles to the west, on the other slope of the 

 Diablo Range, Pliocene deposits are also known to be present in con- 

 siderable thickness. If we assume that erosion and deposition occurred 

 over large areas we must also consider the possibility of having avail- 

 able a sufficiently large land area to supply the required quantity of 

 sediment. A question at once arises as to the possible location of an 

 area large enough to supply by erosion during the Pliocene time sedi- 

 ments sufficient to form strata two miles in thickness. If we consider 

 the present mountain ranges and the Great Valley as practically per- 

 manent structural features since Miocene time, the bringing of any 

 material from the Sierra Nevada to be deposited in shallow water 

 this far away seems out of question. One solution that may be 

 offered is that the sediments were deposited only locally, and that they 

 were derived from the stripping of frequently moving fault-blocks. 

 On the steep sides of these blocks deposits would accumulate very 

 rapidly and probably in considerable thickness. These sediments 

 would, however, be only local. That such conditions existed seems 

 to be suggested by comparison of the great thickness of strata south 

 of Coalinga with a section about fifteen miles distant north of that 

 town. In that area, near Oilfields, the Etchegoin is only 3000 feet in 

 thickness. The Tulare being for the most part covered by alluvium, 

 only small areas of it are exposed. 



Definite evidence for the age of the Etchegoin was first given by 

 Professor J. C. Merriam, 25 who has shown that fossil land mammals 

 found at the base of the lower Etchegoin (" Jacalitos") and at several 

 other higher horizons represent the Pliocene. 



2 5 Merriam, J. C, Tertiary vertebrate faunas of the North Coalinga Eegion 

 of California, Trans. Am. Philos. Soc, vol. 22, pt. 3, 1915. 



