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Abstract Coralville Lake (Fig. 1) was authorized under the Flood Control Act of 1938 as a means of moderating stream flow on the Iowa River. Construction of the dam was begun in 1949, thendelayed by the Korean conflict, and consequently not completed until 1958. Coralville Dam regulates runoff from 3,084 mi 2 (8,018 km 2 ) of land upstream, providing flood protection to 1,703 mi 2 (4,428 km 2 ) of the Iowa River Valley below the dam. The U.S. Army Corps of Engineers maintains Coralville Lake asa multiple-use project providing primary benefits in flood control and low-flow augmentation, and secondary benefits in recreation, fish and wildlife management, forest management, and waterquality improvement. Lake MacBride (Fig. 1) is a subimpoundment of Coralville Lake. The lake and surrounding land compriseLake MacBride State Park, which is managed by he Iowa Conservation Commission. Exposures along the valley walls of that portion of the IowaRiver which comprises Coralville Lake, afford one the opportunity to examine at numerous points along its extent the upper most portion of the Wapsipinicon Formation and the entire Cedar Valley Formation. Excellent exposures of the Coralville Member of the Cedar Valley Formation can also be seen in the valley walls of the Iowa River in Iowa City (Witzke, 1984a).