Surficial geology of the southern half of Griggs County, North Dakota

The southern half of Griggs County, in east-central North Dakota, lies entirely within the Young Drift section of the Central Lowlands physiographic province and is characterized by its undulating surface and nonintegrated drainage. The Kensel, Cooperstown, and Luverne phase of a Late Wisconsinan glaciation are largely responsible for the present appearance of the surface. The tills deposited during glacial stillstands cannot yet be differentiated by texture or X-ray diffreaction analyses, but the average shale pebble content of Kensel till is 16% higher than Cooperstown till. Synthesis of Pleistocene history is based on the distribution of lithostratigraphic units and glacial geomorphic features. Pleistocene lithostratigraphic units include the interbedded silt and clay which were deposited in proglacial lakes, the gravel unit deposited as ice-contact stratified drift, the sand unit or outwash plain deposits, and the slightly stony sandy loam or glacial till. The most widely distributed unit is the slightly stony sandy loam with approximately 9% gravel, 35% sand, 31% silt, and 25% clay withan average composition (mid-range values) of about 35% quartz, 4% plagioclase, 4% K-feldspar, 7% dolomite, 10% calcite, 2% kaolinite, 17% montmorillonite, and 14% illite. Pleistocene sands and gravels in southern Griggs County are economically important for use in construction and as ground water aquifers. The Cooperstown outwash plain is an excellent source of shallow ground water, whereas the Spiritwood aquifer offers an even greater supply. The bedrock valley, containing this latter aquifer, Griggs County. Further test hole drilling is recommended for a more accurate evaluation