1. Isopach and lithofacies map of the Sauk sequence (excluding basal clastics) in the northern midcontinent, U.S.A. Yale Public content 1987. 2002-06-01T04:00:00Z. 2002-06-01T04:00:00Z. Geological Survey (U.S.). The Survey ; For sale by Branch of Distribution. English. Public. Northwest, Old. Ordovician and Cambrian.