Which way to DC?

The scraggly schists and gneisses that rise from this river rapid might deceive you to place this photo somewhere in the United States' mountainous west. But Great Falls Park is actually close to the East Coast, just a short drive (albeit a long paddle) from one of the nation's busiest cities. Keep on the Potomac another 14-ish miles southeast and you'll see familiar buildings like the Washington Monument and Lincoln Memorial break the horizon along its banks. As it flows past Washington, DC, the river opens into a gradually widening tidal passage, eventually emptying into the massive, multi-armed Chesapeake Bay.