lupton: GEOLOGY OF SAN RAFAEL SWELL, UTAH 187 



approached. Badland topography is common, especially near 

 stream courses. 



Structurally, the Swell is an elongated almost flat-topped dome 

 extending northeast and southwest. The dip of the strata along 

 the west flank is generally less than 10°, whereas that almong the 

 east flank is as much as 70°. The strata in the interior of the dome 

 are comparatively flat-lying, the principal line of flexure being 

 near the east flank. Local minor domes were noted along the 

 west side. Faults with displacements ranging up to more than 

 100 feet were observed in and near Cedar Mountain or Red Plateau 

 at the north end of the region. Considerable faulting probably 

 has occurred along the east flank. 



Carboniferous (?), Triassic, Jurassic, and Cretaceous formations 

 are well exposed. The lower part of the section described below 

 was correlated with the section noted by Gilbert in the Henry 

 Mountains regions, whereas the upper part is almost equivalent 

 to the Book Cliffs section to the north. The lowest rocks exposed 

 in this region are represented by a limestone probably of Carbon- 

 iferous age noted by F. L. Hess near the San Rafael River on the 

 east side of the Swell. Above the limestone there is a series of 

 several hundred feet of sandstone and shale interbedded which 

 probably are representatives of the Shinarump group (of Permian 

 and Triassic age) and the Vermilion Cliff sandstone (of Triassic 

 age). Unconformably (?) overlying these beds is a massive much 

 cross-bedded gray sandstone 800 or more feet thick. This is the 

 Gray Cliff sandstone (of Jurrassic age) of Gilbert's Henry Moun- 

 tains section, which forms the striking topography referred to 

 above and is, in all probability, the same as the White Cliff sand- 

 stone of the eastern Uinta and southern Utah sections of Powell. 

 Conformably overlying this sandstone is a sequence of 1350 feet 

 of reddish and gray sandstone, sandy shale, and thick beds of 

 gypsum, which is approximately equivalent to the Flaming Gorge 

 formation of Powell and corresponds closely with the Flaming 

 Gorge formation as described by Gilbert in the Henry Mountains. 

 Five hundred feet of conglomerate, sandstone and sandy shale of 

 greenish drab color, overlying these strata correspond to the larger 

 part of the Henrys Fork formation as identified by Gilbert in the 



