THE MUDDY MOUNTAIN OVERTHRUST IN NEVADA 71 



proximately 9,000 feet, and yet the thrust surface is almost paral- 

 lel to the bedding. The portion of the plate that formerly lay 

 north of the Arrowhead fault has been removed by erosion, whereas 

 on some other sides of Callville Mountain the strata involved in 

 the movement have been carried downward by normal faulting. 



Structural features adjacent to Callville Mouutain. — North of 

 Callville Mountain the Mesozoic rocks form a broad anticline 

 with its axis extending slightly north of west. Lateral move- 

 ment on the White Basin fault has caused displacement of the 

 strata within the anticline, corresponding to the offset in the 

 north boundary of Callville Mountain. To the east the fold 

 plunges beneath Tertiary sediments, and to the west it dies out on 

 meeting a stronger north-south anticline which is overturned toward 

 the east. The north-south fold is affected by a strike fault, and 

 near Callville Mountain the structure is further complicated by 

 overthrusting. An overturned block of Kaibab and Moenkopi 

 limestones has been thrust toward the northeast and now lies di- 

 rectly on the Jurassic sandstone. The thrust plane dips to the 

 southwest at an angle of 60°; but it is possible that its original atti- 

 tude was less steep, and that its present inclination is in part due to 

 tilting during normal faulting which has affected the block. 



One structural feature south of Callville Mountain deserves 

 special mention. Nearly a mile southeast of the Muddy Peaks 

 mass an isolated block of Callville limestone forms a prominent 

 ridge. The beds dip northwest at an angle of 30°, and on the south 

 side the block is faulted down against Jurassic sandstone. This 

 relation, which is similar to that on the north side of Callville Moun- 

 tain, suggests that on the south side also the overthrust plate has 

 been faulted down against younger formations. To what extent 

 this is true cannot be definitely determined, because the Tertiary 

 deposits conceal all except small portions of the older rocks. Pos- 

 sibly the isolated exposure of Callville limestone is only a local 

 feature, with exceptional structural relations. 



DIRECTION OF OVERTHRUSTING 



No striations were found on the poHshed thrust surface to indi- 

 cate direction of movement; but crumpling and minor thrusting in 



