518 REPORT UNITED STATES GEOLOGICAL SURVEY. 



Greek. After crossing Ham's Fork this road ascends the plateau on the 

 west side, and continues its course to the northwest, crossing Bock Creek 

 and following down a branch of Sublette's Creek to the valley of Bear 

 River. At Smith's Fork we left this valley and followed the latter stream 

 to its head where the Lander road crosses it. Turning eastward we 

 crossed via Thompson's Pass to the east side of the mountains. The 

 road keeps south of the southern end of the Wyoming and Salt River 

 Ranges, crossing the high ridges which extend southward. Leaving 

 Smith's Fork the road follows for a short distance down Labarge Creek, 

 but soon comes out on the head of Piney Creek at the north end of 

 Thompson plateau. The eastern edge of this plateau marks the western 

 limit of the Tertiary beds of the Green River Basin. North of the plateau 

 an anticlinal fold (Meridian Fold) in Cretaceous and, perhaps, older beds 

 marks the limit for some distance. The streams from the mountains cut 

 across this anticlinal in canons. . The Thompson platieau is composed of 

 Carboniferous rocks. As we proceed northward the Tertiary strata reach 

 up nearly to the summit of the anticlinal, covering and concealing the 

 eastern half. On the west, between the anticlinal and the mountains, 

 the drainage shows a tendency to north and south courses outside of the 

 main valleys, which are east and west. At the head of the canon cut 

 across the anticlinal the streams are therefore found to have' united. 

 This is very marked in the case of Piney Creek, but is also shown in the 

 streams farther north. The strata between the anticlinal and the mount- 

 ains dip to the westward with, of course, north and south strikes, which, 

 from erosion, gives a series of low hogback ridges. The same right- 

 angled arrangement is seen in the mountains, but to a lesser degree, 

 and it is due to the fact that the Carboniferous limestones also dip to 

 the west. We followed a trail, that was often very dim, from Piney 

 Creek to Lake Creek, and thence across Bitterroot and Lander Creeks 

 to Marsh Creek, keeping between the mountains and the anticlinal ridge 

 already referred to. 



Reaching Marsh Creek, we found a large and well-marked Indian trail 

 leading up the creek. We followed this trail to the head of the creek 

 and across McDougal's Gap. The ascent to the pass is easy and grad- 

 ual. The descent from the summit to the level of McDougal's Creek 

 is abrupt, and for some distance down the creek the trail is very steep 

 and rocky, with some very heavy grades. The canon of McDougal 

 Creek is narrow throughout its entire length, having no alluvial bottoms 

 until the valley of John Day's River is reached. The latter stream sep- 

 arates the Wyoming Range from the Salt River Range. Both ranges are 

 full of first-class mountain peaks. From the mouth of McDougal's Creek 

 we went up John Day's River until we were opposite Wyoming Peak. 

 After making a station on this peak we retraced our steps to the mouth 

 of Sickle Creek, which comes into the river nearly opposite McDougal's 

 Creek. The valley of Johu Day's River is canon-like throughout almost 

 its entire length, and it is well timbered with pine and spruce. The 

 largest area of bottom land is just above the mouth of McDougal's Creek, 

 where an island widens the river. 



We followed Sickle Creek to its head at McDougal's Pass. On the 

 west side of the pass we found a huge snow-bank filling the gorge at the 

 head of Glacier Creek. Several of the side gulches farther down were 

 also found to be filled with snow-banks. The trail down the creek is 

 rough. Not only is it very rocky, but it is also much obstructed by tim- 

 ber. The Salt River range is composed largely of Carboniferous rocks. 

 The change as we emerge from the gloomy canon of Glacier Creek and 

 come out into the broad valley of Salt River is striking. 



