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



but are less distinctly folded than the basal rhyolites. The 

 basalt capping is practically horizontal. 



Canon Rhyolite. — In Virgin Valley, and also at Thousand 

 Creek, the formation underlying the mammal beds consists of 

 rhyolitic Hows. In Virgin Valley this basal series is folded 

 into a syncline containing the Virgin Valley Beds. The rhyo- 

 lites are well exposed on the western side of Virgin Valley at 

 Hard Rock Ridge near Virgin Ranch, where they are dipping 

 gently to the northeast beneath the Virgin Valley Beds. These 

 beds form the sharp gorge through which Virgin Creek enters 

 the valley from the southwest. To the east, the rhyolites form 

 Thousand Creek Ridge, which slopes gently to the southwest 

 and drops off precipitously to the east (see pis. 3 and 4, and 

 text fig. 2). Through this ridge the drainage of the valley 

 escapes in a deep, narrow canon cut by Thousand Creek. At 

 Thousand Creek Canon the rhyolites are exposed to a thickness 

 of not less than four hundred feet and dip gently toward the 

 southwest, or toward the middle of Virgin Valley. 



At the top of the hill above Thousand Creek Canon, the 

 uppermost beds to the south of the wagon road are practically 

 horizontal, and judged from their position possibly represent 

 a phase of the rhyolite laid down after the earlier portion of 

 the formation had been eroded and deformed. From this upper 

 phase much of the rhyolite occurring as pebbles and boulders in 

 the rhyolitic gravels apparently interbedded with the Virgin 

 Valley Beds (see p. 41), seems to have been derived. The 

 rhyolite flows are accompanied by tuffs, which are exceedingly 

 coarse in places, the fragments of pumice in them being in many 

 cases several inches in diameter. 



The precipitous slope on the east side of the rhyolitic out- 

 crop at Thousand Creek Canon is a fault-scrap, the base of 

 which is covered on the east side by the mammal beds of 

 Thousand Creek. On the eastern side of the Thousand Creek 

 basin the same mammal beds rest upon the rhyolites forming the 

 upper portion of the eruptive series on the northwestern flank 

 of the Pueblo Range. 



The rhyolites of Thousand Creek Canon may be traced 

 around the borders of Virgin Valley to the northwest along the 



