OCR Text |
Show CHAPTER VII. THE WASATCH PLATEAU. Situation and structure of the "Wasatch Plateau.â€"Of what strata composed.â€"The great monoclinal.â€" The Cretaceous platform south of it.â€"Salina CaTion.â€"The Jurassic Wedge.â€"East and West Gunnison faults.â€"San Pete Plateau.â€"Sedimentary beds composing the Wasateh Plateau; Bitter Creek, Lower Green River, and Upper Green Eiver beds. The name of Wasatch Plateau has been given to the northernmost of those highlands of tabular form which are the subject of the present monograph. It is in some sense an outlier of the group, and presents features peculiarly its own, though sharing with them a common history and many similar features. It slightly overlaps at its northern end the main range of the Wasatch Mountains, and stands en echelon to the southeast of Mount Nebo, the last great mountain of that beautiful chain. The interval betwreen Nebo and the plateau is about 15 miles, and is filled partly by a medley of low hills and partly by a depression called San Pete Valley, which lies along the base of the table. The western flank of the uplift is a monoclinal flexure of the grandest proportions: Along a base line nearly 50 miles in length the Tertiary strata bend upward to the summit in a single sweep, diversified by minor inequalities arising partly from minor fractures, partly from erosion, but never of such magnitude as to mask the general plan of the uplift, nor even to greatly disfigure its symmetry. The minor features, though elsewhere they might seem of considerable moment, are mere ripples upon the great wave. At the summit the strata suddenly flex back to horizontality, and when we reach it we find ourselves upon a long narrow platform, nowhere more than 6 miles in width, usually much narrower, and here and there reduced to a knife-edge or even eaten through by erosion. To the eastward the profile at once drops down, often by a great cliff, always abruptly, by a succession of leaps across the edges of the sensibly horizontal strata, to lower terraces, succeeding each other at intervals of 3 to 6 miles, and consisting of older and older formations. 160 |