Modeled Top of the Grande Ronde Basalt Geomodel Unit (grtop_f)
The grtop_f grid represents the modeled elevation of the top of the Grande Ronde Basalt geomodel unit 
at a 500 foot resolution. It is one grid of a geomodel that consists of eleven grids and a spatial extent 
polygon shapefile. As part of a U.S. Geological Survey Groundwater Resources Program study, a …