42 EEPOET UNITED STATES GEOLOGICAL SUEVET. 



to the uses of white men were contained within its limits. Lakes, rivers, 

 and streams were seen there, the latter two only for portions of their 

 coiirses, with the exception of the Sweetwater, which was surveyed 

 throughout very nearly its entke course. Few incidents, perhaps, are 

 so gratifying to the exj)lorer as to follow a river from its first soiu-ces 

 down to its mouth. While the Uttle brook first met with can be crossed 

 by a single step, the volume of water is gradually swelled until, finally, 

 it may become a question whether the stream can be forded or must be 

 crossed by swimming. The observations of the v^ddening valley, the in- 

 creasing effect exercised by a growing stream, and the acquauitance 

 with the entire system of drainage, furnish a peculiar satisfaction to any 

 any one making them. 



In the subjoined pages we shall first consider the surface character of 

 the district examined, and then its geological structure. Form and size 

 of the various elevations and depressions, the distribution of water, either 

 flowing or in still bodies, stand in such close relationshix) with the geog- 

 nostic and stratigraphical conditions of every region, that a knowledge 

 of one is requisite ia order to fully appreciate and understand the other. 

 With a view to accomphshing this end to best advantage, a special dis- 

 cussion of the toiDographical features is inserted, which can subsequently 

 be referred to during the description of the geognostic and geological 

 character of any locality under consideration. Without the aid of a map, 

 prepared upon a sufficiently large scale, the only available data are notes 

 and memory. For this reason, much of the detail features observed must 

 necessarily be omitted, and any discussion of topographical structure 

 must be confined within narrow limits. 



TOPOGEAPHY. 



Glancing at a map of Wypmiag, j\^e will usually find a large blank 

 left in its southern central portion. This represents the southern part 

 of our district, lying between west longitude 107 and 109 degrees, and 

 on either side of the forty-second parallel. In its topographical struc- 

 ture this region may be regarded as very uniform. Bluff succeeds bluff 

 ia regular arrangement, retaining about the same relative level. Val- 

 leys varying ia width have- been cut into the yieldiag material which 

 composes them. Only in comparatively rare instances do we find any 

 point reaching a considerably higher elevation than that of its surround- 

 ing. In case we do, its existence is generally due to the influence of 

 volcanic rocks. A number of buttes formed in this manner, rising above 

 the level of the surrounding bluffs, are found along a line extending in a 

 northwesterly direction from Eed Desert station. Their prominence is 

 due to the presence of ejected lavas. In the central region of this uni- 

 formly depressed area we find broad valleys, sometimes containing lakes. 

 Along a certain line, trending a little north of east, there are modifi- 

 cations of the usual forms which are produced by the accumulation of 

 sand. By lying up against the sides of the bluffs, or by forming wave- 

 shaped low hills, the presence of this sand changes the detail-charac- 

 ter of the regions within which it is found. If a general type should be 

 given, indicating the form and distribution of the bluffs within this sec- 

 tion of country^ it might be described as long, narrow ridges, cut trans- 

 versely by fluviatUe erosion. That erosion has shaped the entire surface 

 of this region, there can be no doubt, excepting the isolated places where 

 eruptive activity has stamped its impression. We must regard this por- 

 tion of the Territory as, primarily, a long, even slope to the south, begin- 

 ning at the southern base of the metamorphic elevated area. Erosion 



