In the newly digitized coverage, the USGS altered several units (parts of Mcu, Mbf, Mn, Mpn, and Sb). Where these units were too thin to display on the paper map, they were represented as bold contact lines. These thin units now appear as very thin polygons in the geology spatial database so that unit attributes can be assigned. Dikes and sill also appear as polygons in the geology spatial database since they have been designated as a specific unit and represent the only occurrences of this unit.