Beyond Iowa
Karst limestone and organic-rich black shales are the two geological substrates that produce the most indoor radon, uranium-laden groundwater, and radium-bearing soils in the United States. They concentrate across eight major regions — from the Ozarks and Appalachian valleys to the Marcellus shale and the Colorado Plateau. Click a region on the map to see the geology and the cancer overlay.
Sources: USGS Karst Map 2014 (SIR 2014-5156) · USGS Black Shale Bulletin 1391 · USGS DDS-082 uranium · EPA Map of Radon Zones · CDC US Cancer Statistics 2017–2021 · peer-reviewed studies cited per region.
MO · AR · OK · KS
Mississippian and Ordovician dolomite/limestone — one of the largest karst systems in North America. Lead-zinc Tri-State Mining District sits in dolostone aquifers.
Indoor radon EPA Zone 1/2; legacy lead and cadmium contamination in tailings ('chat'); naturally occurring radium-226 in deep aquifers used for drinking water.
Missouri lung mortality ~46/100k, Arkansas ~50/100k. Tri-State counties have elevated kidney and lung cancer rates linked to lead/cadmium plus radon co-exposure (CDC ATSDR Picher 2010).
Source: USGS Karst Map 2014; ATSDR Tar Creek Superfund 2010.
Iowa, the Dakotas, and Colorado have the highest indoor radon in the US but only middling lung mortality, because smoking prevalence is low. Appalachia stacks Zone-1 geology on top of the country's highest smoking rates, so its lung mortality is double Colorado's.
The Chattanooga, Marcellus, Pierre, and Morrison shales push uranium, radium, and arsenic into shallow wells. Bladder, kidney, and pediatric leukemia signals show up most clearly in counties with high private-well dependence.
Karst dissolution channels move water at meters per hour, not centimeters per day. Agricultural nitrate, pesticide, and radium contamination from one farm can reach a spring miles away within days — concentrating exposure where municipal treatment is weak.
Roughly 520 abandoned uranium mines remain on Navajo land. Lung, kidney, and stomach cancer rates in exposed communities run substantially above the US average, and remediation is decades behind schedule.