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



39 



of movement occurred along this line during Virgin Valley time. 

 The level of the region to the west of the fault-line must have 

 been somewhat higher than that of the country to the east after 

 the basalt outflow in order to permit the establishment of the 

 present drainage system, which flows toward the east across 

 Thousand Creek Ridge. 



The drainage system of Virgin Valley as it now appears is 

 a very interesting feature of the region, as it pursues its course 

 apparently without respect to very prominent barriers (see 

 pi. 2). To the north, west, and east of the valley the streams 

 cut narrow canons through very hard ridges of the older 

 rhyolitic rocks; while the stream-beds in the valley proper are 

 broad, and in some eases widen out into marshy belts. The 

 small stream of Thousand Creek, formed by the union of Virgin 

 and Beet creeks, leaves the broad, open valley to cut straight 

 into the hard rhyolite of Thousand Creek Ridge, through which 

 it passes in a very narrow canon (pis. 3 and 4). It is evident 

 that the barriers crossed by the present drainage were passed in 

 the process of cutting through the Virgin Valley Beds and into 

 the buried ridges of the older formation. The general progress 

 of canon cutting may have been retarded considerably at times 

 by the nature of the opposing barriers and movements along 

 the fault-line crossing the stream at the mouth of Thousand 

 Creek Canon possibly retarded it still farther. 



During the process of excavation of Virgin Valley there 

 appear to have been several resting stages of which some record 

 is left in terraces. At least two levels of terracing seem to be 

 indicated on the slopes of the valley. Both represent levels of 

 relatively slow accumulation of alluvial fans, which have been 

 followed by periods of cutting in which the ends of the older 

 fans have been sharply truncated. The levels of these terraces 

 are about twenty feet and forty feet above the present floor of 

 the valley. 



In the course of excavation of the valley, numerous 

 landslides have evidently been an important feature in the move- 

 ment of material from the walls of the bordering table-lands. 

 On both sides of Virgin Creek numerous large blocks of the 

 mesa with the basalt capping almost intact are seen in various 



