This is an index of county-based mosaics of USGS topographic maps. Map images were derived from scans of USGS 7.5 minute quadrangle maps (Digital Raster Graphics) circa 2000, from which the map collar information was removed. Images are GeoTIFF files in NAD83, UTM zone 18. A DRG is useful as a source or background layer in a GIS, as a means to perform quality assurance on other digital products, and as a source for the collection and revision of DLG data.