THE MUDDY MOUNTAIN OVERTHRUST IN NEVADA 67 



STRUCTURE OF CALLVILLE MOUNTAIN 



Fault boundaries. — Very evidently the steep sides of Callville 

 Mountain are in large part due to normal faulting. Portions of the 

 actual fault surface are well exposed, and at many points the adja- 

 cent younger formations may be seen in fault contact with the 

 Paleozoic rocks of the mountain. The White Basin fault scarp is 

 exceptionally well preserved. Adjacent to White Basin it is sev- 

 eral hundred feet high, and its remarkable regularity gives it the 

 appearance of an artificial wall. At the base of the scarp, Ter- 

 tiary beds are turned steeply upward along the edge of the down- 

 thrown block, and large slickensided surfaces are numerous on the 

 hard Paleozoic hmestone of the footwall. Slickensides are distin- 

 guishable even at a height of more than 100 feet above the base of 

 the cliff. These fault surfaces have an average westward inchna- 

 tion of 50°, and near its southern end the scarp as a whole has 

 the same inclination to a height of nearly 1,000 feet. The un- 

 dissected character of the scarp is due in part to the eastward tilt 

 of the footwall block. Consequent streams on the block flow 

 eastward, and have cut deep canyons across the Rogers Spring 

 fault scarp, which accordingly has a much older appearance 

 than the White Basin scarp. At the base of the Rogers Spring 

 front the Tertiary beds are upturned steeply toward the moun- 

 tain, and portions of the fault plane are exposed, dipping 60° 

 eastward. The block east of the fault has been thrown at least 

 several hundred feet. Thus the part of Callville Mountain included 

 between the Rogers Spring and White Basin faults is a typical horst. 



Similar faults, all with large throw, bound White Basin on the 

 west, and at least a part of the west boundary of Callville Mountain 

 is formed by normal fault scarps. It is very natural, therefore, to 

 infer that the mountain is an irregular horst or group of horsts left 

 elevated by the sinking of adjacent blocks. For the northern 

 boundary, however, this explanation is not tenable. This side of 

 the mountain is high and precipitous, and has the general appear- 

 ance of an eroded fault scarp; but the fault plane, exposed at many 

 points near the base of the chff, has an average dip of nearly 70° to 

 the south, and the older strata of the mountain have very evidently 

 moved down with respect to the younger formations on the north. 



