1. Aeromagnetic maps and terrace magnetization map 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. Northwest, Pacific, Idaho Batholith (Idaho and Mont.), Idaho, and Challis Region.