University of California Publications. [Geology 



extends under a mesa which corresponds in general to the 

 table-lands in the Virgin Valley region. The capping of this 

 mesa is similar to the Mesa Basalt in Virgin Valley. On the 

 northwestern border of the basin large outcrops of ashy beds, 

 apparently representing the later Virgin Valley Beds, are visible 

 beneath the basalt cap. To the east of Thousand Creek Flats 

 the mammal beds come in contact with the upper portion of the 

 Pueblo Range Series. The mammal beds here seem to extend 



Fig. 5. — Section along the C-D line on plate 2, showing section from 

 Thousand Creek Eidge to Railroad Eidge. 



in nearly horizontal position over to the contact with the rather 

 steeply inclined upper beds of the Pueblo Range Series, so that 

 the relation of the two groups of beds is apparently one of 

 unconformity. 



The principal exposures near Thousand Creek consist of 

 tufaceous beds, ashes, and sands, ranging from white to red and 

 dark brown. Many of the strata presumably represent ancient 

 soil accumulations much like that covering the floor of the valley 

 at the present time. Distinctly sandy layers appear a short 

 distance below the top of the section at the northern end of the 

 basin, and also in the beds at the southern extremity near 

 Thousand Creek Ridge. A layer of white to gray ash, one to 

 two feet thick, is exposed low in the section near Thousand Creek 

 Ridge, and one is also seen in the beds at the northern end of the 

 basin. The two may represent the same horizon, but they have 

 not been traced through the series of exposures. Beds of gravel 

 of considerable extent are also present. In some instances the 

 gravels may represent terrace deposits of more recent age than 

 the principal exposures of mammal beds in the basin. 



Both the southern and northern exposures in Thousand Creek 

 basin are truncated by a terrace or mesa having approximately 

 the same level as the top of Railroad Ridge. An exception to 

 this is seen in a prominent hill which rises above this table and 

 above Railroad Ridge in the northern exposures. 



SECTIONC-D 



