Three distinct regions characterize Maryland's topography. The first and major area, falling within the Atlantic Coastal Plain, is nearly bisected by the Chesapeake Bay, dividing Maryland into the Eastern Shore and the Western Shore. The Piedmont Plateau, west of the coastal lowlands, is broad, rolling upland with several deep gorges cut by rivers. Further west, from the Catoctin Mountains in Frederick County to the West Virginia border, is the Appalachian Mountain region, containing the state's highest hills. Backbone Mountain, in Garrett County in westernmost Maryland, is the state's highest point, at 3,360 ft (1,025 m).
A few small islands lie in the Chesapeake Bay, Maryland's dominant waterway. Extending 195 mi (314 km) inland from the Atlantic and varying in width from 3 to 20 mi (5–32 km), the bay comprises 3,237 sq mi (8,384 sq km), of which 1,726 sq km (4,470 sq km) are under Maryland's jurisdiction. Principal rivers include the Potomac, forming much of the southern and western border; the Patapsco, which runs through Baltimore; the Patuxent, draining the Western Shore; and the Susquehanna, crossing the Pennsylvania border and emptying into the Chesapeake Bay in northeastern Maryland. The state has 23 rivers and other bays, as well as many lakes and creeks, none of any great size.