A Selected Study: Forest River Exposure, Inkser, North Dakota
The 30m (98 ft) high Forest River exposure, which is roughly two miles north and two miles west of Inkster, North Dakota, reveals some geologic features that are unique to this part of the state. This study involved two units, a till and an overlying sand, as well as a mass injected into the sand unit. The till unit is a 13.7m (45 ft) thick, structureless unit. Texture analysis averages are: 6.55% gravel; 38.23% sand; 44.53% silt; and 17.31% clay. Coarse sand lithology averages are: shale 41.9%, crystalline 36.1%, dolomite 19.3%, and unknown 2.7%. The overlying sand unit is 6.4m (21 ft) thick and has 18 distinct layers. It contains six reverse faults ranging from 1.04m to 1.83m in length. Texture analysis averages for layers 1 and 3 are: 9.58% gravel; 98.75% sand; 1.25% silt; and 0.00% clay. Coarse sand lithology averages for these layers are: 48.6% shale; 28.5% crystalline; 21.1% dolomite; and 1.9% unknown. A three-pronged injected mass had a total length of 5.48m, and a surface area of 3.0m2. Texture and lithology were identical to those of the underlying till unit. Harris (1993) suggests that the till is equivalent to the "Heiberg'' till, but stratigraphically it is equivalent to the Falconer Formation. Evidence in Ardnt (1977), Hansen and Kume (1970), and Laird (1969) suggested that the sand unit is part of the Elk Valley Delta. The injected mass is interpreted as an upward injected till dike as previously suggested by Dreimanis (1992).
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