Not only do the larger rivers occupy the valley floors, but the soils are thicker, the slopes are gentler, and the valleys are better protected from winter winds. (Farmland is even lighter than usual in this image because the fields are fallow after the harvest.) Geologically, the valleys are the softer, more erodible rock layers, much the preferred places for human settlement. The Appalachian Mountains appear striped because the ridges are forested, providing a dense and dark canopy cover, while the valleys are farmed with crops that generally appear as lighter-toned areas. The farm-dominated Piedmont Plateau is the light-toned area between the mountains and the bay. Cities are difficult to detect from space during daylight hours, so the sickle-shaped bend of the river is a good visual guide for astronauts trying to photograph the nation’s capital, Washington D.C. Sunglint reflections reveal details of Chesapeake Bay and the great bend of the Potomac River. The image shows more than 500 kilometers (300 miles) of this low mountain chain from northeast Pennsylvania (top right) to southern West Virginia, where a dusting of snow covers a patch of land (lower left). This regional view shows the striking visual effect of the valley-and-ridge topography of the Appalachian Mountains as viewed from the International Space Station.
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