Professional Paper - United States Geological Survey Volume 70 (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1911 Excerpt: ...Mountains and of pre-Kenai age, and a lower one, which is of post-Kenai age. He also presents facts pointing to three peneplains in the Yukon region--one marked by the summit of the Coast Range, one by the plateau level here described, and a third which has only a local development. Dawson,3 the first to describe the inland plateau region, recognized one extensive epoch of base-leveling. This took place after the folding of the "Laramie." This "Laramie" has already been correlated with the Alaskan Kenai (p. 103), so that Dawson's peneplain can be provisionally correlated with the one here described. LOWLANDS. The only two extensive lowland areas of the Mount McKinley province are those of the lower Susitna and lower Tanana valleys, which have many features in common. Both have a roughly wedge-shaped outline, with the apex of the angle upstream. The Susitna lowland is bounded on both sides by broad gravel terraces sloping up to high ranges; the Tanana lowland has a similar feature on the south, but on the north abuts against the escarpment which marks the southern edge of the highlands. (See Pl. XIII, A.) The surface of the Susitna lowland slopes toward Cook Inlet at a grade of 5 or 6 feet to the mile. There is also a somewhat steeper slope from the bounding escaqiments toward the axis of the basin, which is approximately the position occupied by Susitna River. The gradient of the Tanana lowland between the gravel escaqiment on the south and the base of the upland on the north is about 10 feet to the mile, while its downstream slope toward the Yukon is less than 2 feet to the mile. As a consequence Tanana River closely hugs the north wall of the valley and its southerly tributaries are madly rushing, overloaded streams, while those from t...