The Willow Creek district, Alaska Volume 606-610

 
9781231067949: The Willow Creek district, Alaska Volume 606-610
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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. 1915 Excerpt: ...material, consisting of coarse cobbles and large bowlders of diorite, arkose, and conglomerate, has remained. None of the tributaries of Little Susitna River have important recent gravel deposits, and all of them flow through channels filled with large bowlders. (See PI. XI, A.) Willow Creek has built up a valley floor of stream gravels below the mouth of Homestake Creek, and the stream flat gradually increases in width toward the west. The low gradient of the valley here has permitted the deposition of gravels derived from the postglacial cuts of the stream above. The stream deposits consist for the most part of cobbles, finer gravel, and sand, but include numerous bowlders a foot or two in diameter and a few larger bowlders. Grubstake and Wet gulches contain considerable deposits of stream-laid material in the intermediate portions of their valleys between the steep lower stretches and the cirques in which they head. IGNEOUS BOCKS. GRANITIC AND GNEISSIC ROCKS. DISTRIBUTION. As has already been stated, the northern half of this district consists of granitic intrusive rocks, which are a part of the great intrusive mass that comprises a large portion of the Talkeetna Mountains. As mapped by Paige and Knopf 1 the area in which these rocks predominate measures about 35 by 50 miles, and the Willow Creek district lies on its southern edge. The upper basins of Shorty, Craigie, Willow, and Fishhook creeks lie within this area; the basins of Archangel and Reed creeks contain no other rocks, and probably the entire headward portion of Little Susitna Valley is eroded into the intrusive mass, for all the stream bowlders were derived from granitic rocks. Between the head of Willow Creek and the east edge of this 1 Paige, Sidney, and Knopf, Adolph, Geologic reconnaissan...

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