1 Arc-second Digital Elevation Models (DEMs) - USGS National Map 3DEP Downloadable
               Data Collection
This is a tiled collection of the 3D Elevation Program (3DEP) and is 1 arc-second
            (approximately 30 m) resolution. The elevations in this Digital Elevation Model (DEM)
            represent the topographic bare-earth surface. The 3DEP data holdings serve as the
            elevation layer of The National …