400 Mountain Upthrusts. 
The great Uinta fold has usually been described as terminating 
abruptly in Northwestern Colorado. As a conspicuous fold it does 
so terminate there; but continuous with its axis to the eastward 
there is a long, gentle anticlinal, which reaches by a broad curve to 
the foot-hills of the Park Range—a western porton of the Rocky 
Mountain system. This I regard as a continuation of the Uinta fold 
far beyond its reputed termination, and also, in connection with other 
facts, as indicating structural relationship between the Uinta and 
Park Ranges. I therefore divide the Uinta fold into two portions— 
namely, the Uinta fold proper, and the inceptive portion of the 
same, 
The Uinta fold proper is about one hundred and fifty miles in 
length, and from thirty to forty miles in width at the extreme limit 
of the upturned strata at either side. Its western end is blended 
with the Wasatch Range in Utah, which it meets at nearly right 
angles. Its eastern terminus is about thirty miles within, and east 
of, the western boundary of Colorado, and about the same distance 
from the northern boundary. Its axis, except the slight southward 
inclination ofits eastern end, is approximately cast and west, and 
at nearly right angles with that of the Park Range. 
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Fig, 1.—A generalized section across the Uinta Fold. 
This great fold is remarkable for its simplicity, its almost entire 
freedom from lateral complications, and for the extent of its vertical 
displacement. Its type of uplift is also peculiar, the sides being 
abrupt and the top broadly cunvex. The accompanying generalized 
section across the fold (Fig. 1) indicates its general character, and 
also shows the formations which are involved in it. 
