Sinkholes, hydrogeology, and groundwater quality in northeast Iowa, G. R. Hallberg and B. E. Hoyer, 1982, 120 p., 19 figs., 13 tables, 13 pl., 9 appendices. The Open-File Report series consists of interim reports from a variety of ongoing studies, including contract studies with various State and Federal agencies. These reports often have a limited distribution.