- National Atlas of the United States39
- Geological Survey (U.S.)33
- Arndt, Raymond E.10
- Bawiec, Walter J.10
- Beikman, Helen M.10
- King, Philip B.10
- National Geophysical Data Center10
- Schruben, Paul G.10
- Geological Survey (U.S.) Minerals Information Team9
- University of Iowa. Libraries. Map Collection4
- EROS Data Center3
- Gap Analysis Program (U.S.)3
- Godt, Jonathan W.3
- Anderson Publishing Company2
- State Historical Society of Iowa (Iowa City)2
- United States. Forest Service2
- Wade, Tim2
- Advocate-Republican1
- Andreas, A. T. (Alfred Theodore), 1839-19001
- Blackburn, Laura1
