UTAH LAKE EEGION. 345 



on the west. In Timpanogos Peak, the average rise of its slope, from the 

 foot-hills to the summit, is more than one in three for an elevation of 7,500 

 feet, while the upper 5,000 feet of the ridge rise almost one in one, pre- 

 senting a wall so steep that, but for the shelf-like projections on its surface, 

 resulting from the horizontality of its beds, it would be dangerous to climb. 



It will be seen by reference to the map that the general shape of the 

 western slope of the ridge is that of a pair of steps, the first rise being of 

 about 3,000 feet to an outlying shoulder, from which the main ridge rises, 

 about 2 miles farther back, in a steep, almost perpendicular, wall. Here 

 again, as so frequently in the Rocky Mountain region, the physical structure 

 gives the clue to the geological. Timpanogos Peak is formed of horizon- 

 tally-bedded limestones, having at the most an inclination of 3° east and 1° 

 or 2° to the south. These beds are found to increase in dip a few miles 

 farther east, and disappear beneath overlying members of the Carboniferous 

 formation, to which they belong; but, on the west, their continuity is 

 abruptly broken, nor could one imagine an erosion which would leave an 

 abrupt wall of 7,500 feet in height on one side of a valley nearly 20 miles 

 wide. The topography suggests that the line of junction of this lower 

 shoulder with the face of the upper wall is that of a line of fault, and this 

 idea is confirmed, as will be seen later, by the finding of faultings in the 

 canons of the Provo and American Fork, at either end of the ridge, in corre- 

 sponding position. 



In the ridge of Provo Peaks, the continuance of this line of fault is 

 shown also in the topography, as well as rendered necessary by the thick- 

 ness of the strata observed; while a second line of faulting along the very 

 foot-hills, with the downthrow, as seems to be universally the case in this 

 range, on the west, together with the sharp crushing of the strata into an 

 S-shaped fold, which has preceded and given rise to the dislocation, is 

 shown in the section exposed in the little canon of Rock Creek back of 

 Provo City. 



As the face of the hills on either side of Rock Canon shows nearly hori- 

 zontal lines of stratification, like that of Timpanogos Peak, the observer, on 

 entering the caiion, and finding in its bottom clay-slates and quartzites 

 standing perpendicularly, and even with a slight westerly dip, is at first led 

 to believe that he has here a series of rocks entirely unconformable to the 



