DOG VALLBT. 189 



to the country at large may be comprised in the statement that it is an 

 excellent illustration of what Powell has called the Kaibab structure. 

 The length from north to south cannot be definitely given until we can fix 

 its northern boundary, which, if done at all, must be done arbitrarily, for 

 it fades out so gradually that no real demarkation exists. The same may 

 be said of its eastern boundary. But assuming the plateau to extend 

 northward to the base of the Tushar and eastward to the Sevier Plateau, 

 the length would be about 50 miles and the breadth about 28 miles. 



The greater part of this area is covered with ancient eruptions resting 

 upon Tertiary lacustrine beds. Around the southern and western sides of 

 the plateau the sedimentary strata project several miles beyond the volcanic 

 sheets and end abruptly in giant cliffs, facing the south and west, and 

 deeply scored by erosion. The western wall of the plateau is formed by 

 the northward prolongation of the Hurricane fault, while the southern wall 

 consists of cliffs of erosion without any known dislocation of great magni- 

 tude. These southern cliffs are the lingering remnants of Tertiary and 

 Cretaceous beds, which once extended over the entire region to the south- 

 ward beyond the Colorado, but have throughout Tertiary time receded 

 by waste to their present boundary. 



The detailed description will begin at the northern portion. At the 

 foot of the lofty summits which crown the southern end of the Tushar 

 lies Dog Valley, inclosed south and west by rolling and somewhat rugged 

 volcanic hills and by remnants of a great volcanic conglomerate. Similar 

 hills are found to the eastward, and the whole tract is a center or focus of 

 eruptions of the trachytic epoch. The cones and craters which may once 

 have existed are no longer visible, having been wasted to a medley of hills 

 by a period of decay which stretches far back towards middle Tertiary 

 time. Soil and gravel, with a rich growth of wild grass and shrubbery, 

 now mantle these degraded remnants, giving them a rather pleasant and 

 gentle aspect. Yet the outcrops of volcanic sheets around the borders and 

 away from the valley betray its history in spite of the effort of nature to 

 hide it. East, west, and south the old floods are seen to radiate away for 

 many miles from this center, spreading out and growing thinner as they 

 were poured along over the ancient inequalities of the land. They also 



