DRG

http://tahoe.usgs.gov/DRG.html

A Digital Raster Graphic (DRG) is a digital image (scanned version) of a USGS topographic map. DRGs are produced from USGS 1:24,000-, 1:24,000/1:25,000-, 1:63,360- (Alaska), 1:100,000-, and 1:250,000-scale topographic map series. The image inside the map neatline is georeferenced to the surface of the Earth and fit to the Universal Transverse Mercator (UTM) projection. Pictured is the Lake Tahoe Basin.