230 EEPORT UNITED STATES GEOLOGICAL SURVEY. 



but they are unmistakable in tlieir litliological characteristics, and yet 

 tlie latter does not liere form a hogback as it usually does elsewhere. 



Proceeding westward from Ashley's Fork my journey, after the first 

 three or four miles, was over the Uinta Group until we reached Lake 

 Fork. This groui^ is much more extensively develoi)ed in this region 

 than I have anywhere seen'it before. It is many hundred feet in tldck- 

 uess, and it is qidte as regularly stratified as any of the other fresh water 

 Tertiary deposits of the West. In some places, as for example, in the 

 vicinity of Green Eiver, south of the Uinta Mountains, it is largelj'' 

 composed of soft, bad-land sandstones, having a general reddish color. 

 But further westward it assumes a somewhat darker hue and character 

 of quite regularly bedded sandstones, some of which are soft, but many 

 of the strata are firm and even massive. At Wonsitz Ridge, four miles 

 west of Dodds's Ranch, it rests unconformably upon the Laramie Gi'oup, 

 and at Lake Fork on the Uinta and Salt Lake trail, some forty miles 

 further west, it is found to rest upon the Bridger Group, as it was shown 

 to do near White River, in my report for 1870. 



'No fossils of any kind were found by myself in the Unita Group this 

 year, but in 1875, 1 obtained a Physa from it in the valley of Snake River, 

 a few miles above Junction Mountain. The Uinta Group, as already 

 shown, is regarded as equivalent with the Brown's Parle Group of 

 Powell 5 and it is x)robablv also equivalent with the Lake Beds of Middle 

 Park. 



Three or four hundred feet in thickness of the strata of the Bridger 

 Group are exposed in the valley side of Lake Fork, which have there aU 

 the jieculiar lithological characteristics which they possess at the typical 

 localities north of the Uinta Mountains, even including the A^arious tints 

 of coloration and the style of weathering of the bad-land sandstones of 

 which the formation is largely composed. From these strata I made a 

 A'^ery good collection of vertebrate fossils, consisting of Ganoid, Chelonian 

 and Mammalian remains, but the only invertebrate form I discovered 

 was the well known Planorhis JJtaliensis Meek (= P. spectabiHs Meek.) 



Following the trail, the course of which lies south of the wagon-road, 

 to the east fork of the Duchesne, I found near the crossing some limited 

 exposures of Bridger strata in its valley side, with those of the Uinta 

 Group resting ujjon them, biit I obtained no fossils there. Still follow- 

 ing the obscure trail before mentioned, our journey from the east fork 

 of the Duchesne to the main stream was OA^er sandy barrens v/ith here 

 and there an exposure of sandstone. Upon reaching the latter stream 

 I found it to run in a cabon or deep monoclinal A^alley excaA^ated out of 

 the Green River Grouj). The dip of these strata at the A^alley where I 

 examined it is three or four degrees to the northward or northeastAvard, 

 but as they are seen in the high hills south of the A^alley the dip seems 

 to be considerably more there. This dip seems to be i^art of a broad 

 accessory fold, subordinate to the Uinta Mountain ui)lift, by which these 

 Green River strata haA^e risen from beneath those of the Bridger Group 

 that were seen on Lake Fork and the east fork of the Duchesne. No 

 fossils were found in these Green River strata although diligent search 

 was made, but the lithological characteristics are the same as they are 

 at the typical localities north of the Uinta Mountains, the upper and 

 lower divisions of the group being plainly recognizable. The thickness 

 of the group as seen in this region is estimated at about 1,000 feet, but 

 as the base was not visible where the upper diA^sion was obserA^ecl, the 

 entire thickness of the group here is probably equal to that which it 

 attains at the typical localities. The canon of the Duchesne, where I 

 observed it, has high precipitous sides, and is in all respects like that 



