G42 EEPOET UNITED STATES GEOLOGICAL SURVEY. 



Creek Yalley. They iucline a few degrees, but this is probably dne to 

 deposition and not to a movement after their deposition. 



Marsh Creek Group. — These beds as exposed on Marsh Creek above 

 Eed Eock Gap are very white, friable sandstones, which dip a degree or 

 two from the mountains. Farther down the valley they are covered by 

 the basalt flow. They are probably older than the dei)Osits I have in- 

 cluded under the Cache Yalley Group. 



Gentile Valley Group. — Near one of our sub-stations in Gentile Valley 

 a coarse conglomerate outcrops, which was horizontal and seemed to be 

 older than the soft deposits in the centre of the valley. In the Portneuf 

 Canon a similar conglomerate was noted, and also on the east side of 

 Cache Valley. These beds I have iDrovisionally designated the Gentile 

 Valley Group. 



I have not the space here to enter into any detailed description of the 

 groups just mentioned. The reader is referred to Chapters IV and V for 

 further details. That all the beds were deposited in fresh- water lakes 

 there is no doubt. A \dew of the valley, in which they are found and 

 their fossils indicate this. They represent a part of the great basin of 

 which the Great Salt Lake Valley is a part. This fact was long ago 

 recognized by Dr. Hayden. In the report for 1870 he says : 



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

 Lake Valley forms only a part. We sliall find tliat what is tei'med tbe 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 

 mone of them are much above the level of the waters of Great Salt Lake. (P. 172.) 



I infer that a vast fresh-water lake once occupied all this immeuse basin ; that the 

 smaller ranges of mountains were scattered over it as isolated islands, their summits 

 projecting above the surface ; that the waters have gradually and slowly passed away 

 %j evaporation, and the terraces left to reveal certain oscillations of level and the 

 steps of x^rogress toward the present order of things ; and that the briny waters have 

 concentrated in those lake basins, which have no outlet. (P. 170.) 



The fact that Cache Valley was covered by one of these lakes was first 

 indicated by Dr. Hayden in 1871*. To it should be added Marsh Val- 

 ley, Gentile Valley, and Basalt and Upper Portneuf Valleys, and, pos- 

 sibly, the region of the Blackfoot, although the latter is now completely 

 covered with basalt. The lake in this latter region probably connected 

 with the Marsh Valley lake by way of the Portneuf Canon, while Eed 

 Eock Gap, or Pass, was the i3oint of structure connecting the lake of 

 Cache Valley with that of Marsh Creek Valley. The point of outlet of 

 the Marsh Valley lake was evidently somewhere beyond the junction of 

 Marsh Creek and the Portneuf Eiver. The axis of the Baunack Eange 

 probably formed tlie barrier which, when it was eroded low enough, al- 

 lowed the Marsh Valley lake to be completely drained. The latter was 

 probably a much shallower lake than that of Cache Valley. After it 

 was drained the barrier was at Eed Eock Gap. The elevation on both 

 sides of the pass is about 5,000 feet or a little less, and the level of the 

 lake, as indicated by the upper terraces, was at lirst about 5800 feet. 

 When it reached the level of the Bonneville Beach it was 5,185.7 feet. 

 The elevation of the Provo Beach was about 4,825.7 feet; so that when 

 the gap was eroded below that elevation, the lake of the Provo level 

 was drained from Cache Valley. 



^Eept. U. S. Geol. Siu'vey for 1871, 1872, p. 19. 



