The 1:24,000-scale DEM data archived here at the EROS site is divided just like 7.5′ paper maps into 7.5 x 7.5-minute sets indexed by the USGS quadrangle name. Use the FTP by Alphabetical List site if the name of the USGS map is known. If the name of the map is not known, use the FTP via Graphics to search for the desired data. The data is registered using metric UTM values according to NAD27. Grid cell elevations are presented in meters.