68 University of California Publications in Geology [Vol. 7 



forms, in its flightless character suggesting to the author of the 

 species an insular breeding-ground free from enemies, and 

 finally in the fact that the accompanying molluscan fauna in- 

 dicates a climate cooler than that which characterizes the region 

 at present. It is regretable that a larger number of species was 

 not discovered in the same horizon. 



Pleistocene Fauna 



Potter Creek Cave. — Potter Creek Cave 8 takes its Iname 

 from its location on Potter Creek, about one mile east of Baird, 

 a station of the U. S. Bureau of Fisheries on the McCloud River 

 in Shasta County, California. The locality lies at present in 

 the lower Transition zone at an elevation of 1500 feet above the 

 sea. The surrounding country is well timbered with conifers, 

 oaks, and maples in the main, and with lower scrub forming 

 thickets in less favorable exposure. Topographically the region 

 is rendered rather rough by numerous small tributaries of the 

 McCloud River cutting through the Baird Shales, and the 

 McCloud Limestones, to form canons with abrupt slopes and 

 much dissected ridges. The cave occupies at present a position 

 800 feet above the McCloud River, only slightly over a mile away. 



According to the observations of Sinclair, the river flowed 

 during the formation of the cavern deposits at approximately 

 the level of the cave floor. The lowering of the river bed and 

 the backward cutting of tributary streams brought about more 

 rapid drainage of the country to either side of the cave, less 

 water entered the fissure, and cave-cutting ceased. Openings 

 were formed later in the roof of the cave by surface erosion, 

 thus permitting the entrance of clay, rock fragments, broken 

 bones and possibly of live animals. Subsequent uplift increased 

 the cutting by streams in the region, and Potter Creek cut 

 down through one of the galleries, thus forming the present cave 

 entrance. 



There were two or three of these periods of uplift as deter- 

 mined by Sinclair which changed the character of the country 

 from one of moderate relief to one of mountainous aspect dis- 



8 See Sinclair, W. J., Univ. Calif. Publ. Am. Arch. Ethn., vol. 2, pp. 

 1-27, 1904. 



