Great Salt Lake (GSL), Utah, lost 1.89 +/- 0.04 meters of water during the 2012 to 2016 drought. During this timeframe, data from the GRACE mission do not detect anomalous mass loss, but nearby Global Positioning System (GPS) stations show significant shifts in position. We find that crustal deformation, from unloading the Earth’s crust with the observed GSL water loss alone, does not explain the GPS displacements, suggesting contributions from additional water storage loss surrounding GSL. This study applies a damped least squares inversion to the 3D GPS displacements to test a range of distributions of radial mass load rings to fit the observations. When considering the horizontal and vertical displacements simultaneously, we find the most realistic distribution of water loss while also resolving the observed water loss of the lake. Our preferred model identifies radially decreasing mass loss up to 64 km from the lake. The contribution of exterior groundwater loss is substantial (10.9 +/- 2.8 km^3 vs. 5.5 +/- 1.0 km^3 on the lake), and greatly improves the fit to the observations. Nearby groundwater wells exhibit significant water loss during the drought, which substantiates the presence of significant water loss outside of the lake, but also highlights greater spatial variation than our model can resolve. We observe seismicity modulation within the inferred load region, while the region outside the (un)loading reveals no significant modulation. Drier periods exhibit higher quantities of events than wetter periods and changes in trend of the earthquake rate are correlated with regional mass trends.