Trail of Preparation - The geology encountered by Lewis during his trip from Washington to Pittsburgh encompassed an entire cross section of the Appalachian. From the Piedmont at Washington he crossed the Blue Ridge to Harpers Ferry, then through the heart of the Appalachians to Ft. Ashby, Virginia (currently West Virginia). From there he ascended and crossed the Appalachian Plateaus to Pittsburgh (geology relief from USGS Time and Terrain).