GENERAL STRUCTUEE OF THE WASATCH PLATEAU. 161 



The eastern front of the plateau is simply a wall left standing by the erosion 

 of the region which it faces. The Tertiary beds upon the summit, as well 

 as the Cretaceous beneath, once spread, unbroken and undisturbed, as far 

 to the eastward as the eye can reach, and thence far beyond the limits of 

 vision. From the strange land which that summit now overlooks at an 

 altitude of 11,500 feet, more than 8,000 feet of Tertiary and Mesozoic 

 strata have been swept away, and the region which has been thus devas- 

 tated is large enough for a great kingdom. The Wasatch Plateau is a 

 mere remnant of that protracted process, and, so far as it extends, is a 

 mere rim standing along a portion of the western boundary of the Plateau 

 Province. 



The western front of the plateau, then, is a great monoclinal flexure, 

 and its eastern front is a wall of erosion. To the northward the beds which 

 compose it stretch far up toward the Uinta Mountains, still ending in lines 

 of great cliffs or bold slopes gradually swinging to the eastward until, after 

 a course of nearly a hundred miles, they cross the Green River, where 

 Powell named the Tertiaries the Roan Cliffs, and the Upper Cretaceous 

 the Book Cliffs. Southward the Tertiaries forming the summit of the 

 plateau end abruptly in a' precipice extending east and west, while the 

 underlying Cretaceous beds continue, forming a lower terrace overlooking 

 the still lower level of Castle Valley. The average altitude of the table is 

 about 11,000 feet, and it stands from 5,500 to 6,000 feet above San Pete 

 Valley on the west and about the same height above Castle Valley on the 

 east. To gain an adequate conception of the great monoclinal, which forms 

 the western flank, we must recur to the consideration that the upward 

 curvature and reflection to horizontally leaves the Lower Tertiary beds full 

 5,500 feet above still more recent ones in the valley below. If the latter 

 were now continuous across the summit, as they once probably were, the 

 altitude would be from 1,500 to 2,000 feet greater than at present. Thus 

 the total rise of the monoclinal appears to have been more than 7,000 feet, 

 and the uplift has occurred with a near approach to equality along a line 

 of strike of 50 miles. The transverse structure will be seen by referring 

 to Plate 3, sections 6 and 7. 



The platform of the summit is rugged, the irregularities being due 



11 H P 



