1. Complete Bouguer gravity, isostatic residual gravity, and related geophysical maps centered on the Idaho Batholith and Challis volcanic field, northwestern United States Yale Public content 1992. 2002-06-01T04:00:00Z. 2002-06-01T04:00:00Z. Geological Survey (U.S.). The Survey ; For sale by Map Distribution. English. Public. Idaho, Montana, and Idaho Batholith (Idaho and Mont.).