100 GEOLOGICAL SUEVEY OF THE TERRITORIES. 



G-rand, immediately opposite the plateau in which station 48 was lo- 

 cated. Its course is nearly south, on a line with Coal Creek. The valley 

 is comparatively narrow, there being but tew open bottoms along its 

 course. The slopes of the hills on either side are well timbered with 

 pines and cottonwoods. Near the head of the main creek there are 

 large bowlders of a black basalt, derived, in all probability, from the 

 layer which once covered the entire divide. While on this creek we 

 met a party of prospectors, who said they had found indications of gold 

 along the stream, but not in any very great quantity. 



The divide between Eock Creek and this branch of the liTorth Fork is 

 a sharp ridge of Cretaceous sandstones, reaching above the timber-line. 

 The strata dip about 15° to the west, the angle decreasing on crossing 

 theNorth Fork, until they become almost horizontal in theplateau divide 

 between North Fork of the Gunnison and Grand Eiver. Station 20 was 

 located on this ridge. The lines of outcrop between the station and 

 Sopris peak are the prolongation of the hog-backs on the west side of 

 Eoariug Fork. 



The rock on the summit of station 26 is a compact greenish-gray 

 sandstone, somewhat laminated, and containing in the lower part frag- 

 ments of stems and leaves, and particles of carbonaceous material. The 

 most careful search revealed nothing jjerfect enough for identification. Be- 

 low this sandstone is a narrow baud of dark-colored, very compact lime- 

 stone, of a reddish-brown color on the weathered surfaces. Next below is 

 a coarse textured, soft, gray sandstone, which seemed to continue to the 

 base of the amphitheater which the station overlooked. 



Near the base of the slope we ascended, I noticed an outcrop of con- 

 glomerate in which the pebbles were of a rock very much like that form- 

 ing the nucleus of the Elk Mountains. The matrix was siliceous. 

 What the relations of this bed were to the sandstones I could not de- 

 termine, as the slopes were covered with a heavy growth of timber, and 

 the underlying beds were for the most part covered with debris. The 

 pebbles were rounded and evidently water-worn. 



South of station 26 the strike curves to the eastward, the dip changing 

 more and more toward the southwest. The line of outcrop of the Creta- 

 ceous beds crosses Eock Creek into the Elk Mountains, where they become 

 very much faulted and upturned. In this portion of the Elk Mountains 

 Dr. Hayden made a more detailed survey, and to his report and the re- 

 port of Mr. Holmes, the reader is referred for the geology of Eock Creek 

 and the adjacent peaks. 



Station 33 was located south of station 26 on one of a group of high 

 peaks, rising from a mass of trachyte resembling that composing the 

 mountains between Anthracite Creek and the head of Ohio Creek near 

 station 32. 



The western slope of this mass is extremely steep, the sandstone 

 reaching to the base , almost horizontal in position. At the northern 

 end, however, as seen from a distance, the strata appear to dip to the 

 northeast at an angle of about 40°, so that there would seem to be a 

 synclinal fold between this point and the ridge, extending from station 

 26. A branch of North Fork rises here and flows nearly due west. Near 

 its mouth the beds are also inclined towards the. northwest, although 

 the angle is only about 5°. 



At the southern end of the mass in which station 33 is situated, on 

 Anthracite Creek, the sandstones are tipped up, dipping north 54P west 

 at an angle of 15°. Dikes of trachyte penetrate the sandstones. The branch 

 of North Fork that we have just been considering, after the union of the 



