1. Bouguer gravity anomaly map and geologic interpretation of the Iron River 1⁰?x 2⁰?quadrangle, Michigan and Wisconsin [cartographic material] Yale Public content 1989. 2002-06-01T04:00:00Z. 2016-01-11T18:20:48Z. Geological Survey (U.S.). The Survey ; For sale by Map Distribution. English. Public. Michigan and Wisconsin.