172 GEOLOGICAL SURVEY OF THE TERRITORIES. 



We might note, in this connection, many changes which this valley 

 must have been subjected to since the present configuration of the sur- 

 face was outlined by the elevation of the mountain chains. Several 

 times this valley must have been filled high up on the mountain sides 

 with water ; water, too, with but very little of that saline character which 

 it possesses at this time. Indeed, I am convinced that, while the lake 

 itself is not of modern origin, yet as a salt lake, in its present condition, 

 it is of comparatively recent date. We find all along the flanks of the 

 mountains, and high up in the valleys of the ravines opening into this 

 basin, groups of strata hundreds of feet in thickness, which are doubtless 

 of fresh-water origin, dating back into the pliocene or upper tertiary 

 period. Then these beds have been disturbed by the elevations of the 

 mountains, showing that while these ranges formed shore lines for the 

 lakes of this period, they did not reach their present height until after 

 the deposition of these tertiary beds. Eesting upon them, and appar- 

 ently deposited after the upheaval movements had ceased, are heavy 

 beds of sand and gravel, and the flanks of the mountains all around the 

 valley, as well as the sides of the mountains in the islands of the lake, 

 reveal numerous water lines, showing most clearly the elevations to 

 which the waters of the lake must have reached in later geological times. 

 We can hardly suppose that during these periods the waters here were 

 sufficiently salt to differ from the other lakes in the West. I am inclined 

 to the belief, therefore, that the saline materials of a vast area have been 

 concentrated by time into the basin now occupied by Salt Lake, and 

 that it is owing to its partial evaporation that its water is become so salt. 



Let us for a moment take a bird's-eye view of the great inland basin 

 of which Salt Lake Valley forms only a part. We shall find that what 

 is termed the Great Basin of the West comprises the vast area inclosed 

 by the Wasatch Mountains on the east, and the Sierra Nevada on the 

 west, the crest or water divide of the Columbia on the north, and that 

 of the Colorado on the south. We shall also observe that this great 

 region has no visible outlet; that it is composed of a multitude of 

 smaller basins or valleys, each of which has its little lakes, springs, and 

 water-courses, their surplus water either evaporating or sinking beneath 

 the surface. If we examine the elevations in this region, we observe a 

 wonderful uniformity in the surface of the valleys, and find that none 

 of them are much above the level of the waters of Great Salt Lake. As 

 Captain Stansbury has remarked: 



These plains are but little elevated above the present level of the lake, and have, 

 beyond question, at one time formed a part of it ; an elevation of but a few feet above 

 the present level of the lake would float this entire flat to a great distance, thus forming 

 a vast inland sea. 



It seems probable, also, that at a comparatively modern period the 

 briny waters spread out over a much larger area than at present, 

 for both Fremont and Stansbury make frequent mention of large tracts 

 covered with an incrustation of salt. The latter, in describing the broad 

 plain country to the west of Great Salt Lake, says : 



The first part of the plain consisted simply of dried mud, with small crystals of salt 

 scattered thickly over the surface. Crossing this, -we came upon another portion of it, 

 three miles in width, where the ground was entirely covered with a thin layer of salt 

 in a state of deliquescence, and of so soft a consistence that the feet of our mules sank 

 at every step into the mud beneath. But we soon came upon a portion of the plain 

 where the salt lay in a solid state in one unbroken sheet, extending, apparently, to its 

 western border. So firm and strong was this unique and snowy floor, that it sustained 

 the weight of our entire train without in the least giving way or cracking beneath the 

 pressure. Our mules walked upon it as upon a sheet of solid ice. The whole field was 

 crossed by a network of little ridges, projecting about half an inch, as if the salt had 

 expanded in the process of crystalization. I estimated this field to be at least seven 



