WHITE.] DISPLACEMENTS. 45 



ever,^is preserved in only a part of it, the remaiuder being narrowed 

 by the erosion of Fox Creek Valley, and in part modified by the spur- 

 like termination of both ends. 



The width of Plateau Uplift varies from about five, to ten miles ; and 

 its extreme length as a mountain elevation is about forty-five miles. It 

 is widest at its western end, where it terminates by two great spurs or 

 mountain ridges, namely, Split Mountain and Section Ridge, each of 

 which has a westward-dipping anticlinal axis, and consequently a parti- 

 versal* dip of its strata. At its eastern end, however, it terminates by 

 ouly one dipping anticlinal, with its abrupt partiversal dip, the sweep 

 of which is broader than that of the two western oues. The eastern 

 end of the Plateau Uplift extends so far eastward as to blend with the 

 terminal mountain mass of the axial portion of the Uinta Range. The 

 intimate connection of the Plateau Uplift with that of the main Uinta 

 axis will be understood by the statement that the two are separated 

 only by a sharp synclinal axis, which is in part a fault. The maximum 

 amount of this displacement is fully 2,000 feet ; but in some places, 

 nevertheless, the mountain masses of the two uplifts are blended to- 

 gether topographically just as the Midland Uplift, presently to be de- 

 scribed, is in part blended with the Plateau Uplitt. The mass of the 

 latter uplift is, however, in large part separated topographically from 

 that of the Axial Uplift by the deep Eed Eock Basin, described on a 

 previous page, and by the eastward prolongation of that basin in the 

 form of a mountain valley. The two great spurs which project from 

 the western end of Yampa Plateau, with their rapidly-dipping anti- 

 clinal axes and the regular partiversal dip of their strata, are remark- 

 able for their magnitude as well as for their inherent peculiarities. They 

 are really great mountain masses, their summits being more than 3,000 

 feet above the neighboring portion of Green Eiver, which traverses 

 Split Mountain by a profound caiion, as has been described on a pre- 

 vious page of this report. 



llie Midland Uplift. — The amount of displacement which took place 

 in the elevation of this uplift is nearly 5,000 feet from the strata of the 

 Colorado Group which flank it immediately to the southward, and which 

 remain there comparatively undisturbed ; and yet this displacement is 

 about 3,000 feet less than that of Plateau Uplift, -with which Midland 

 Uplift lies parallel and in close contact. The influence of the latter up- 

 lift extended still farther eastward ; but it is onlj^ the mountain portion 

 that is specially discussed under this head. This portion constitutes 

 the topographical feature I have called Midland Eidge, as well as a 

 part of Yampa Plateau, with which it is continuous. The strata exposed 

 to view by the Midland Uplift are almost wholly those of the Jura-Trias 

 groups. Those sti'ata that have been definitely referred to the Jurassic 

 period, as well as those of the Dakota Group, flank the uplift all along 

 its southern border 5 and upon the highest portion of the Eidge there is 

 also a small area that is capped by these strata. The red beds of the 

 Jura-Trias have been much exposed by erosion in a very large part of 

 the Eidge, their bright colors and great elevation above the surround- 

 ing country making very conspicuous and striking features of the land- 

 scape. The mountain portion of Midland Uplift, the eastern part of 

 which I have called Midland Eidge, does not extend so far eastward 

 as the mountain masses of the plateau and great axial uplifts do ; but 

 as a flexure, Midland Uplift extends much farther eastward. Its axis 

 also makes a bend to the southward in the course of its eastward exten- 

 sion, somewhat like that of the eastward extension of the Axial Uplift ; 



* See foot-note on page 42. 



