Radon gas forms by the radioactive decay of uranium in rock and soil. Radon exposure has been linked to lung cancer and while there’s no safe level of exposure, the current level at which mitigation is recommended is 4pCi/L. Radon is a problem in the Portland Basin due to uranium-rich sediments associated with the ice age Missoula Floods which deposited coarse and fine-grained sediments. Coarse-grained sediments are typically associated with higher levels of indoor radon, which is commonly explained by coarse grained sediments being more permeable, allowing radon gas to escape more quickly. The aim of this project was to evaluate whether depth to groundwater could be a possible control of indoor radon concentrations (IRC). We looked for correlations between IRC and the underlying sediments (coarse vs fine-grained) and the depth to groundwater. Data sources we used included OHA Indoor radon test results, DOGAMI O-18-01 report of radon potential, Geologic Map 3443 of the greater Portland Metropolitan Area, and USGS Scientific Investigations Report 2008– 5059 for depth to groundwater. We created geographic polygons based on sediment type and examined how radon levels within these polygons correlated with sediment type and depth to groundwater. Using this method, we discovered a stronger correlation between IRC and depth to water table than between IRC and sediment type, suggesting sediment size may not be the only control of IRC. Further research using more consistent spatial control is required to verify these initial results based on qualitative spatial averaging.