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Dickinson Dam

Photo of Dickinson Dam and E.A. Patterson Lake
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Dickinson Unit
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Bedrock underlying Dickinson Dam and appurtenant structures is the Sentinel Butte Formation of Paleocene age.  It is a deltaic deposit composed primarily of fine-grained sandstone, siltstone, shales and lignite beds.  Locally overlying the Sentinel Butt are undifferentiated Pleistocene terrace deposits.  They range in composition from silty sand to sandy gravel and can be distinguished from other deposits by their coarse texture, color and rich calcareous content. Terrace deposits covered the bedrock over approximately one-half of the auxiliary spillway area prior to excavation.  Topsoil in the area ranges from 0.3 to 5.8 feet deep with an average depth of approximately 2.0 feet.  It generally consists of fine silty sand, silty sand and clayey sand.

Last updated: Mar 29, 2013