1917] Nomland: The Etchegoin Pliocene of Middle California 203 



beds and the presence of remains of land mammals in some areas. This 

 is also shown by the character of the marine fauna, consisting of such 

 species as Macoma nasuta, Solen sicarius, and Littorina mariana. 

 Hence the transition would be only normal if the basin continued to 

 be filled. The fresh-water beds with Anodonta and other fresh-water 

 forms found by the writer near the base of the Etchegoin and the 

 marine beds discovered by Arnold and Anderson in the Tulare indi- 

 cate that only a slight oscillation was necessary to change from land 

 to marine condition or the reverse during the time-interval represented 

 by the two formations. 



If towards the close of the Etchegoin there was a gradual filling 

 up of the Etchegoin basin and fresh-water conditions finally prevailed, 

 it is evident that this could not have taken place at all points in the 

 district at the same time. Therefore, if the transition is gradual and 

 not represented by unconformity, the line of separation between the 

 two formations would represent only approximately the same period 

 of time in such widely separated areas as Priest Valley, Kettleman 

 Hills, and Arroyo Honda. 



Thickness 



As already stated, the Pliocene in the region studied is of unusual 

 thickness. The lower Etchegoin (" Jacalitos") as measured by Arnold 

 and Anderson at Jacalitos Creek was 3800 feet thick. This figure 

 should be reduced somewhat, because it includes a part of the beds 

 below the unconformity described in the present paper. This would, 

 however, diminish the total thickness only slightly. On Canoas Creek, 

 a few miles south of Jacalitos Creek, the upper Etchegoin measured 

 3600 feet. A maximum thickness of 3100 feet of Tulare, as measured 

 by Arnold and Anderson, was found in the Kettleman Hills near the 

 Dudley-Lemoore road. According to these measured sections, the 

 aggregate thickness of the Pliocene south of Coalinga would be 10,500 

 feet. This is by far the thickest Pliocene section known in America. 

 Heretofore the greatest thickness known has been the Merced Series, 

 a few miles south of San Francisco, California. According to Pro- 

 fessor A. C. Lawson, 24 the total thickness of this series is 5834 feet. 



The question naturally suggests itself as to what were the possible 

 conditions under which this great thickness of strata was deposited. 

 The lower 6700 feet, or the Etchegoin group, is predominantly of 



24 Lawson, A. C, The post-Pliocene diastrophism of the coast of Southern 

 California, Univ. Calif. Publ. Bull. Dept. Geol., vol. 1, p. 147, 1893. 



