Vol. 6] Merriam: Virgin Valley and Thousand Creek. 



43 



land-slides between these gravel beds and the present bed of 

 Virgin Creek. If at an early stage in its history, the main 

 stream had occupied the position in which the gravels are now- 

 situated, it must since then have cut to the south and east across 

 the present valley. If this had occurred, the numerous remnants 

 of slides from the mesa wall, which lie between the rhyolitic 

 gravels and the present stream would necessarily have been 

 removed. As a possible alternative the slides might be supposed 

 to have travelled across the rhyolitic gravels and down into 

 their present positions. This is certainly a violent assumption, 

 as the slides are now separated from the mesa by one or two 

 miles of relatively flat territory. 



The weight of evidence seems to indicate that the rhyolitic 

 gravels were deposited after a short stage of erosion which 

 occurred during the general period of sedimentation charac- 

 terized as the Virgin Valley epoch. This theory receives support 

 from an observation by Mr. Furlong, who has noted the occur- 

 rence of beds of gravel and boulders in the face of some of the 

 exposures of the Virgin Valley Beds one or two miles north 

 of the main occurrence of the gravels. The exposures observed 

 by Furlong were at about the same general level below the mesa 

 as the main outcrop of the rhyolitic gravels. The gravel and 

 boulders were interbedded with the ash strata, and as nearly as 

 the writer can judge from Furlong's description they were of 

 much the same nature as the main rhyolitic gravel outcrops. 



THOUSAND GREEK BEDS. 



In the region immediately to the east of Thousand Creek 

 Ridge there are extensive exposures of mammal-bearing beds 

 bordering the basin known as Thousand ('reek Flats. Large 

 outcrops of these beds are present along the eastern base of 

 Thousand Creek Ridge, and similar beds reach for many miles 

 north from Thousand Creek. A long, narrow, lava-capped mesa 

 known as Railroad Ridge extending nearly north and south for 

 six or seven miles into the Thousand Creek basin is composed of 

 similar beds (pi. 2 and text fig. 5). To the north of the 

 Thousand Creek basin, near a prominent point known as Oregon 

 End, the sedimentary series of Thousand Creek Flats apparently 



