wmmj SURFACE FEATURES VALLEYS. 15 



northern side, especially, sloping gently up to the high lands, while the 

 southern side is formed by the steeper slope of the long high ridge that 

 constitutes the water-shed between the Yampa and Williams Fork. 

 The dip of the strata, which are those of the Laramie Group, is to the 

 northward, and this portion of the valley is therefore a monoclinal one. 

 The widening of the valley here is doubtless due to the softer condition 

 of the strata of that group in this vicinity than those of the same form- 

 ation have farther southward and westward in this district. Much of 

 the bottom-land of this part of the valley is irrigable and the rapid fall 

 of the stream renders its irrigation easily practicable. 



Near the confluence of Williams Fork, and for three or four miles 

 below that point, the valley is narrowed by the encroachment of the 

 bluffs, which are there composed of the strata of the Fox Hills and Lar- 

 amie groups, those of the latter group being less soft there than they 

 are farther up the valley, as before mentioned. In some places within 

 these few miles of the narrowed valley, the sides are so steep as to give 

 it the character of a canon. This is particularly the case just above 

 Canon Park, where the river makes a very abrupt bend among the hills. 



Canon Park. — This is a very small park, and is chiefly noticeable be- 

 cause of its occurrence iu a portion of the valley that is otherwise very 

 narrow, the sides of which are steep and rocky ; and also because of its 

 relation to the geological structure of the neighborhood. The occur- 

 rence of this small park here is evidently due to the crossing of the 

 river by a synclinal flexure or sag of the strata that has thrown the 

 comparatively soft strata of the Laramie and Wasatch groups across 

 the course of the valley, and out of these the park has been excavated, 

 while the harder strata of the Fox Hills and lower portion of the Lar- 

 amie Group form caiion-walls, or high, steep valley-sides above and below. 



Between Caiion Park and the point where the river makes its exit 

 through the bluffs into Axial Basin, which point is about six miles east 

 of Yampa Mountain, the valley is tortuous and very narrow, being, in 

 fact, a caiion along the greater part of the distance. The sides of the 

 valley in this part of its course are so steep and high that, except at 

 a few favorable places, access to the river from the high lands by a mule- 

 train is difficult or impossible. This portion of the valley is excavated 

 out of the strata of the Fox Hills and Laramie groups, those of the 

 former group constituting, iu great part, the south side, and those of 

 the latter the north side of the valley. 



Westward from the point where the river makes its exit through the 

 bluffs into Axial Basin, it pursues a meandering course through the ba- 

 sin a distance that in a straight line is about six miles to Yampa Moun- 

 tain. Here, instead of passing into the western portion of Axial Basin 

 through the comparatively low space at the north side of Yampa Moun- 

 tain, it cuts through the northern portion of that mountain by a deep 

 canon. After thus cutting through the mountain, the river meanders 

 through the broad western portion of Axial Basin some 15 or 18 miles 

 to Junction Mountain, through which it cuts its way by a still deeper 

 and more precipitous caiion than the one by which it passes through 

 Yampa Mountain. These two mountains are, as before stated, isolated 

 upthrusts of Paleozoic rocks through surrounding Cretaceous strata that 

 lie exposed iu the Axial Basin, and are located directly upon the line of 

 the axis of the Uinta Mountain chain. Iu neither case is there any su- 

 perficially apparent reason why the river should not have run around, 

 instead of through the mountain, for the surface around the base of 

 each of them has only a comparativdy slight elevation above the sur- 

 face of the river, amounting, indeed, to only a fraction of the height of 



