Mexico separates the westward-flowing Ohio River watershed from the eastward-flowing watersheds of the Susquehanna, Potomac, and James rivers. A number of eastward-flowing creeks and rivers have their headwaters incised into Allegheny Front, displacing the Divide westward from the Front, including the North Branch of the Potomac River west of Cumberland, Maryland, which originates well into the Appalachian Plateau at the Fairfax Stone, just south of Maryland's southwestern tip. No waterway crosses the Front from east to west. Course in detail The Allegheny Front begins in central Pennsylvania just northwest of the town of Lock Haven and extends southwest paralleling, first, Bald Eagle Mountain, and then Brush Mountain to its east. The Front continues to a point a little north of the Pennsylvania/Maryland boundary where it is offset about to the east as it changes from the bold escarpment that characterized it west of Altoona to its more gentle rise in Maryland. Across the Mason–Dixon line in Maryland, the Front becomes Dans Mountain, west of Cumberland, which reaches in elevation at Dan's Rock. Along Maryland's southern border, the North Branch of the Potomac River cuts down through the Front at just west of Keyser, West Virginia. South of the Potomac, in West Virginia, the Front continues through the Mount Storm area, then passes along the eastern edge of Dolly Sods, a wide plateau of Pottsville conglomerate bedrock at about elevation. From the Sods, the front continues southward as an increasingly steep escarpment west of the North Fork of the South Branch of the Potomac River, with the Roaring Plains continuing the high plateaus of the Dolly Sods area along the escarpment's crest. The Allegheny Front's southern end is Mount Porte Crayon (), after which the land drops steeply to Seneca Creek, west of Seneca Rocks. Escarpments southward South of Mount Porte Crayon and Seneca Creek, the Appalachian Structural Front is less clearly unified. Pottsville-capped Spruce Mountain, south and east of Seneca Creek, continues the Allegheny Front's geology southward; this ridge reaches an elevation of at Spruce Knob, West Virginia's highest point. Similarly steep escarpments sharing much of the same geologic structure are also present nearby along the eastern slopes of Allegheny Mountain and Back Allegheny Mountain (along with the southern end of Shavers Mountain), but these mountains lack the Pottsville caps characteristic of the Allegheny Front. Allegheny Mountain's long, nearly level crest is generally about in elevation, with Paddy Knob reaching