Gaps of the Allegheny - USGS - Appalachians Mountain chain The lines of the barrier ridges in central, western, and northwestern Pennsylvania and their impact on any desired travel or transport in the days before automotive vehicles, or railroads should be obvious.  The travel story gets worse. Counting the Hudson Valley north of the Catskills in New York and the southern end of the chain on the Georgian plains, there are exactly three narrow areas where water gaps allowed climbing up to mountain passes allowing passage across the mountains was possible to animal pulled transport vehicles.
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