History and Geography
Part of the Appalachian Mountains chain, the region does not consist of true mountains, geologically speaking, but instead a dissected plateau that is part of the Allegheny Plateau. The Catskill Mountains are the highest expression of the plateau, located to the east of the Endless Mountains, and separated from them by the Delaware River.
The current geography was slightly modified during the last ice age by the Wisconsin Glacier about 15,000 years ago. Glacial striations can be found on the rocks of some of the high ridges, but the area was at the margin of the ice sheet, and the impact was much less than in New York just to the north.
The "mountains" are made up of sedimentary rocks (mostly sandstone and shales, with a little conglomerate) that were part of a lowland that collected sediments eroded from mountains to the southeast in Mississippian and Pennsylvanian geologic time. The area has been uplifted and lowered several times. The highest points are all nearly the same elevation, establishing that the area had once been eroded into a nearly level peneplane, which has since been uplifted. The present Susquehanna River established its meandering course during that time, when it was a mature stream on a topography of very low relief. When the area was uplifted, the river's bends were preserved as incised meanders. The large river cut a deep valley and established a low baseline for its tributaries, which then cut the plateau into the rugged hills of the present day.
Read more about this topic: Endless Mountains
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