68 



C. R. KEYES INTEEMONT PLAINS OF THE ARID REGION 



Fe. Deep stream-erosion across the valley and many wells indicate 

 clearl)' the character and thin cover of the rock-floor. 



Although the surface of these plains is very smooth and is apparently 

 everywhere covered by mountain wash, the thiclcness of the soft mantle 

 is rarely over 100 feet. The indurated rocks which form the foundation 

 of the plains are often inclined at high angles and are evenly beveled. A 

 typical cross-section is shown near the Hagan coal camp (Una de Gato), 



, Figure 2. — Beveled Plains — Surface of Cretacic Sandstones 



on the east side of the Sandia range, and is represented below (figure 2). 

 The height represented by the section is about 600 feet. The outcrops 

 of the section extend almost continuously for a distance of 20 miles along 

 the Arroyo San Pedro. A similar section of upturned and beveled Cre- 

 tacic strata is esposed near the town of Los Cerrillos. In the vicinity 

 the same phenomenon is repeated hundreds of times. 



LAS VEGAS OF NEVADA 



"The Meadows" of southern Nevada constitute a vast even plain bor- 

 dered by lofty mountains. Eastward from the town of Las Vegas ex- 

 tends a long arm of these plains, which, as it passes between two ranges 

 and joins Meadow valley to the east, is 6 to 8 miles wide. In this arm 

 of the plain the geologic structure is well displayed (figure 3). 

 w / 



Figure 3. — Geologic Cross-section of the Vegas Range, Nevada 



The attitude of the rocks and the relations of the beveled rock-floor to 

 the overlying wash deposits are more clearly shown than immediately to 

 the east or to the west. Still farther to the eastward, in Meadow valley, 

 where there is a perennial stream occupying its middle, a narrow and 

 deep canyon lias been cut in the old bolson. Tertiary deposits are in- 



