Modeled Top of the Overburden Geomodel Unit (obtop_f)
The obtop_f grid represents the modeled elevation of the top of the Overburden 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 three-dimensional …