HATDEN.] 



GEOLOGY SAWATCH RANGE. 53 



above the lakes or valley. For about fifteen miles the Arkansas flows 

 through a gorge-like channel, commencing about four miles above 

 Lake Creek, when there is a moderate expansion with quite a broad 

 bottom, and on either side well-defined terraces. The terrace on the east 

 side of the Arkansas rises about 500 feet above the river-bed. In a dry 

 giilch the horizontal strata of sandstone crop out, showing that it is 

 composed of the modern lake-deposit. On the west side the first ter- 

 race rises 40 feet, the lower portions of the second or main terrace 250 feet 

 rising up, by a slope to the mountains, to the height of 700 feet. One 

 gulch is quite wide, half a mile, as it opens into the valley of the Arkan- 

 sas, with small, terrace-like steps on either side. The east fork of the 

 Arkausas also presents a broad, open valley for some distance along its 

 junction with the main stream. Passing up the west branch we find a 

 broad, open, meadow-like park, a mile in width, with the granitoid rocks 

 cropping out here and there on either side from beneath the great accu- 

 mulation of detrital deposits. 



We can see, therefore, that this entire valley of the Upper Arkansas 

 was at no very remote geological period, a fresh-water lake, pix)bably 

 at the close of the glacial period. I am now inclined to think that this 

 period extended back further into the past in the Rocky Mountains than 

 geologists have accredited it in other regions. It seems to me that the 

 evidence, though not clear as yet, points to the Pliocene era as its begin- 

 ning, at least, and that it extended pretty well toward the present 

 period. It was evidently a period in which powerful forces were in 

 operation, which carved out the surface-forms much as we find them at 

 the present time. 



CHAPTEE III. 



SAWATCH KANGE — MORAINAL DEPOSITS OF TAYLOE'S CREEK — ELK 



MOUNTAINS, ETC. 



We will now ascend the valley of Lake Creek, and wend our way 

 over the great Sawatch range. The valley of Lake Creek is filled with, 

 the morainal deposits for which this range is so remarkable. It would 

 seem that the great glacial force moved here in a direction a little 

 south of east, inasmuch as the great mass of the detrital matter is 

 heaped up on the south side. The two lakes are about 350 yards 

 apart, with a small stream, perhaps 20 feet wide, flowing from one 

 to the other. The interval is made, up of worn detrital matter, but 

 over it and around both lakes are mounds or oblong ridges of the drift. 

 Scattered over the surface are masses of granite, coarse in texture, with 

 crystals of feldspar, 1 and 2 inches in dimensions, aggregated to- 

 gether. The rock has the appearance of a feldspathic breccia. The 

 lower lake is about two and. a half miles in length, and one and a 

 half miles in width. The upper lake is one mile in length, and half 

 a mile in width. The bases of both these lakes are undoubtedly 

 the result of glacial action. The greatest depth found by sound- 

 ing was 76 feet. The accompanying topographical sketch of Mr. 

 Gannett, with the soundings which were made by Messrs. Stevenson 

 and Holmes, will convey a true idea of the form of these basins. We 

 know by the land contiguous to both these lakes that they have been 

 slowly diminishing in area. Above the Upper Twin Lake there is a half- 

 mile in width of boggy meadow which at no distant period must have 

 been covered by the lake. At the head of the valley, or where the 



