This is an earthcache, so there is no physical hide, but you must observe the location, answer some questions, and attach a photo to your log as proof of your visit. There are sidewalks on both sides of the bridge. To cross to get a better view, there is a pedestrian crossing at M St. on the Georgetown side.
Questions: E-mail or message me with the answers to these questions:
1) Choose any one aspect (e.g.,flatness of surrounding land, steepness of banks, presence of structures on the riverside, vegetation on the riverside, or exposed rocks in the river) and contrast the view upstream with the view downstream.
2) You crossed the C&O Canal, which passes under the bridge on the Georgetown side (often it's dry). Explain how the location of the start of this canal in Georgetown relates to the Fall Line.
3) Include a picture of yourself (face not required) or a personal item on the Key Bridge with the Potomac River in the background as proof of your visit. It can be looking upstream or downstream. Any point above the river on the bridge can be used for observation. The posted coordinates are just a suggestion. There are pathways on both sides of the bridge, but crossing the traffic on the bridge itself would be illegal and unsafe.
Description:
For geologists, the Fall Line marks the border between the Atlantic Coastal Plain and the Piedmont. The Coastal Plain has softer, more easily erodible rocks, a flatter terrain, alluvial soils, and sedimentary rocks and the river is usually slower flowing and close to sea level. Much of the sediments of the Coastal Plain came from erosion of the Blue Ridge and Appalachian Highlands further west. The Piedmont represents the foothills of the higher and more mountainous areas further west. Compared to the Coastal Plain, the Piedmont has harder, more resistant rocks, is at a higher altitude, and is steeper and rockier. These features have many implications - such as whether that part of the river is tidal, the type of soils, and the varieties of plants and wildlife.
Source: USGS
For the colonial settlers, the Fall Line marked the location where shipping movements became restricted by waterfalls, rocks, and rapids. Hence, Georgetown and Alexandria were established as ports located just downstream of the Fall Line on the Potomac River. Some of the historic industrial buildings are still observable in Georgetown between K and M Sts. NW. At the Fall Line, the steeper areas nearby upstream provided fast-moving streams that powered mills but were still close to deeper waters for shipping. The Fall Line joins up all these points from East Coast rivers; the Google article on the Fall Line lists 23 East Coast cities and their rivers, including Philadelphia PA, Baltimore MD, Richmond VA, Raleigh NC, and Columbia SC. Interstate 95 approximately follows the Fall Line.
The Fall Line can be better thought of as a zone, with a range of changes over a wider area than a single point on the river. The prominent waterfalls are Little Falls and Great Falls, which are both upstream from this point, but looking upstream and downstream here from the Key Bridge will show some of the geographical contrasts.
Maryland Physiographic Provinces, also showing the District of Columbia; The Fall Line is marked in red. Source: Maryland Department of Natural Resources.
References:
Wikipedia - Fall Line
Virginia Places: Geology of the Fall Line
Maryland Geology