The Mineral Development Atlas (MDA) was a joint project by the United State Geological Survey (USGS), the United States Bureau of Mines (USBM), and the state surveys of Wisconsin, Illinois, and Iowa, and was launched in 1945 to gather information about mining and exploration in the lead-zinc district. The Atlas consists of section maps at 1:2400 scale showing exploration and mining activity in the lead-zinc district of the Upper Mississippi Valley. When the USGS offices in Platteville, WI closed, the Atlas was distributed to the states. The Wisconsin portion covers primarily Grant, Iowa, and Lafayette Counties, and WGNHS is currently working towards making the Wisconsin portion of the Atlas publicly available online. The Iowa County portion of the Atlas contains these GIS layers: 354 section maps showing surface and sub-surface mining activity (compiled in 1 layer), surveyed workings, unsurveyed workings, lead diggings, and boreholes. Item level metadata has been created for surveyed and unsurveyed workings, lead diggings (at or near the surface), and boreholes. Borehole data includes stratigraphy and assay values where available.