A 4,800 mi dune field occupies lowlands in central Alaska in a roughly triangular area between the lower Nowitna River. Nenana, and the Alaska Range. The field can be divided into two tracts: (1) the Northwestern Tract, which extends 90 mi west-southwestward from the Tanana River and is separated from the Southeastern Tract by the Kuskokwim Mountains; (2) the Southeastern Tract, which extends southwest from the Tanana River and is 160 mi long and a maximum of 50 mi wide. The Southeastern Tract is subdivided by the Kantishna and Muddy Rivers into eastern, central, and southwestern areas. The field is composed mostly of parabolic and longitudinal dunes that are 10 to 150 ft high, 50 ft to 3 mi long, and 50 to 1,000 ft wide. The dunes are blanketed by loess and forested with birch or aspen; black spruce and muskeg cover the permanently frozen terrain between the dunes. Sand from many dunes in the Southeastern Tract and from cutbanks of the Kantishna River was sampled; no organic matter, sand wedges, or ice wedges were found, and the sand is generally well sorted, light yellowish gray, and fine grained. It is composed of quartz and chert with some darker rock and mineral grains. Many samples contain a finesilt-and-clay fraction that causes the distribution curve to be bimodal. The eastern area in the vicinity of Dune Lake has a sharply defined sand sheet 50 mi long overlain by irregular transverse dunes that in turn are capped by rosettes, small arcuate dunes arranged concentrically in roughly circular groups about 1 mi in diameter. They seem to be caused by a combination of local and regional winds. The central area is the largest in area and in volume of sand and contains a few large transverse dunes as well as parabolic and longitudinal ridges; the southwestern area has only the latter. Underlying deposits are exposed along the Kantishna River and consist of alluvial sand and silt underlain by gravel. Apparently contemporaneous with the aeolian sand are thick silt deposits on the northeast flanks of Bearpaw Mountain and of Castle Rocks, isolated hills that are southwest of the eastern area and south of the southwestern area of the dune field, respectively. Shape, orientation, and distribution of the dunes and the silt deposits indicate deposition by wind from the northeast. The source of the sand is undoubtedly the Alaska Range, which furnished alluvium to the north-flowing tributaries of the Tanana River. Dune distribution also suggests a barren landscape near the Tanana River, with scattered clumps of vegetation farther from the source of the sand. Present evidence is consistent with the tentative conclusion that the dunes were deposited in late Wisconsin time. A proposed agricultural development in some townships west of Nenana will disturb the thin vegetative and soil cover and may reactivate dune movement.
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