WHITE.] SURFACE FEATURES VALLEYS. 13 



are obstructed by a thick growth of bushes. The valley varies in breadth, 

 widening in some places to form the parks before mentioned, while in 

 other places it is narrowed to a caiion, especially where the Green Kiver 

 Group occupies both sides of the river. 



Agency Park. — Just above White Elver Indian agency the river cuts 

 through the sandstone strata of the Dakota Group, which there dip to 

 the northward and norhtwestward at a considerable angle. The dip, how- 

 ever, soon diminishes, so that for a space of several miles below tbe soft 

 strata of the Colorado Group occupy the surface. Out of these strata 

 Agency Park has been excavated, a portion of them still occupying its 

 surface; the upper layers of the Dakota Group appearing within the 

 park only at one locality, which is on the right bank of the river, near 

 the middle of the park. This park is bounded on the north by a line of 

 escarpment blufis of the Fox Hills Group; on the east and south by hills of 

 Cretaceous strata that lie at the western toot of the White Eiver Plateau j 

 and on the west by the Grand Hogback, which is composed of the 

 upturned strata of the Fox Hills and Laramie Groups and separates 

 Agency, from PowelFs Park. 



Besides several dry drainage-channels that traverse Agency Park to 

 White River, there is one brook of perennial water. This rises in the 

 hills to the eastward, and flows through the park two or three miles and 

 empties into the river upon its right bank. Only a small proportion of the 

 surface of any of the parks lies within reach of irrigating- water from the 

 rivers that run through them, but, in consequence of the somewhat rapid 

 fall of White Kiver, a considerable area within the limits of Agency 

 Park lies within reach of water that may be conducted in irrigating- 

 • ditches. Besides the water that may be thus taken from the river for 

 irrigating purposes, the brook before referred to may also be made to 

 furnish a small but, under the circumstances, valuable addition. There 

 are some broad level spaces within the limits of the ijark, the surfaces 

 of which are at various heights, a hundred feet or more, above the level 

 of the river, that cannot be reached by irrigating- water from it, although 

 they constitute a part of the park surface proper. These have somewhat 

 the appearance of morainal benches, especially as they are usually more 

 or less thickly strewn with drift-pebbles ; but they are composed of the 

 undisturbed strata out of which the park has been excavated. They 

 doubtless represent periodical base-levels of erosion that were succes- 

 sively reached during the excavation of the valley, for they are of vari- 

 ous heights above the level of tbe river and are common in all the broader 

 j>ortions of all the river- valleys of this region. 



PowelVs Parle. — This park lies immediately west of Agency Park, 

 with which it is connected by a gap in the Grand Hogback, through 

 which White River flows. Its name is given in commemoration of the 

 fact that Professor J. W. Powell and his party spent a winter here during 

 his early exploration of this region. It is excavated out of the bad-land 

 strata of the Wasatch Group which flank the Grand Hogback, and pass 

 by a monoclinal flexure beneath the hills which border it to the west- 

 ward, and which are composed of Green River strata. This park is only 

 four or five miles wide from east to west; but as it communicates with a 

 long dry drainage-valley that extends to the northward, and also a simi- 

 lar but smaller one that extends to the southward, its length north and 

 south is great compared with its width, although its boundaries are soi^e- 

 what indefinite. The greater portion of the irrigable land of the park 

 lies on the north side of the river, and consequently within the limits of 

 this district. It is Hogback Valley that is continuous with that portion 

 of Powell's Park which lies within this district, the drainage of which 



