186 lupton: geology of san kafael swell, utah 



( i. K. Gilbert, in his monograph on "The Geology of the Henry 

 Mountains, Utah," C. E. Dutton, in "The High Plateaus of 

 Utah," and J. A. TafT, in Bulletin U. S. Geological Survey No. 

 285, refer briefly to this geologic feature. Other than the short 

 statements in these reports the writer is unaware of any geological 

 literature on this region. 



During the field season of 1911, F. L. Hess spent two days on 

 the east flank of the Swell on San Rafael River. References to 

 that portion of the region are based on his observations. A party 

 under the supervision of the writer, during the same season, 

 mapped in detail the Upper Jurassic and Lower Cretaceous rocks 

 along the west flank of the Swell in Castle Valley. In August, 

 1911, in company with W. R. Calvert, the north end of the region 

 in the vicinity of Cedar Mountain or Red Plateau was visited. 

 A little later accompanied by W. C. Mendenhall the writer entered 

 the interior of the dome. At the close of the field season a recon- 

 naissance trip was made with B. W. Clark to the north end of the 

 Henry Mountains region, at which time the southern end of the 

 San Rafael Swell was crossed. The observations made on these 

 and other excursions form the basis of. these notes. 



The most prominent feature of the topography of this region 

 is a series of buttes, mesas and "castles" which encircle an area, 

 locally known as "Sinbad," which is 40 to 50 miles long and 10 to 

 20 miles in width. These fantastically eroded forms represent 

 the outcrop of a gray massive cross-bedded Jurassic sandstone 

 800 feet thick. It is practicable to cross the Swell at only a few 

 places on account of the almost impassable barrier formed by the 

 sandstone rim. Nearly vertical scarps and canyon walls 300 to 

 500 feet in height are not unusual. The buttes and "castles," 

 above referred to, are conspicuously shown on the San Rafael 

 topographic sheet. Low "hogbacks," formed by resistant beds 

 in the overlying strata, the tops of which produce dip slopes of 

 varying extent depending on the inclination of the beds, encircle 

 this belt of rugged topography. A view to the west from the 

 interior of the Swell gives one the impression of looking up a very 

 gently inclined varicolored stairway, the steps of which increase 

 in height as the top, represented by the Wasatch Plateau, is 



