354 WALTER C. MEN DEN HALL 



effect of erosive or solvent action since the waters left them, and the 

 sandy beach, molded by the waves of the lake upon the alluvial fans 

 which formed a large part of its shores, is still well enough preserved 

 to be readily traced. Only the most modern gullies have cut it away. 

 At one point a low sea cHff notched by the waves in steep alluvial-fan 

 material still stands, as perfectly preserved as though the waters had 

 just withdrawn. 



CONCLUSION 



In conclusion it is to be said that but the barest outlines of the 

 history of this fascinating region are yet known. Its rocks contain 

 a rich upper Miocene fauna, probably in large part new, and its 

 exposures and structures are so clear that its geology will be an open 

 book to the fortunate student to whom falls the pleasant task of 

 deciphering it in detail. 



FOSSIL LOCALITIES' 



Shells are very abundant in the vicinity of Yuha Oil Well, but the variety is 

 not as great here as at other localities where collections were made. A few 

 hundred yards west of the well is an outcrop of an oyster bed which makes a 

 conspicuous shell mound and other similar outcrops exist in the vicinity. 



The horizon is the highest at which collections were made. It is probably 

 a few thousand feet above the Carrizo and Black mountain horizons. Collec- 

 tions Nos. i6o and i6i were made near Yuha Well, and No. 162 was made 

 about one and one-half miles southeast, but the horizons are not believed to be 

 far apart. 



Collection No. 165 is from a point about two miles east of the base of Carrizo 

 Mountain. Shells are abundant here but species are limited, as is true of the 

 vicinity of Yuha Well. These shells are probably stratigraphically lower than 

 collections Nos. 160-62 but are higher than the others except possibly No. 168. 



Collection No. 168 was made on the county road, near "Barrett's Oil Well. 

 The locaUty is nearly midway between Carrizo and Black mountains and must 

 be from substantially the same horizon as Blake's original collection. It is also 

 near the horizon of No. 165, but may be slightly lower. 



No. 163 is from a small arroyo just east of Alverson Canyon, on the south 

 side of Carrizo Mountain. The shells were taken from the yellow clays which 

 immediately overHe the basal conglomerate. These clays contain a rich fauna 

 which is not by any means fully represented in the collection. Stratigraphically 

 these beds belong above the three collections yet to be mentioned. The length 

 of the time interval between the two horizons depends upon the extent of the 



I These descriptive notes are introduced for the use of the paleontologists who may 

 eventually study the collections now in the U.S. National Museum. 



