These mountains are characterized by long, even ridges, with
long, continuous valleys in between. From a great enough
altitude, they almost look like corduroy, except that the widths
of the valleys are somewhat variable and ridges sometimes meet
in a vee. The ridge and valley system presents an important
obstacle to east-west land travel even with today's technology
and was a nearly insurmountable barrier to railroads crossing
the range and especially to underfunded migrants traveling west
to settle the Ohio Country, Northwest Territory and Oregon
Country, before the days of motorized transportation. In the era
when animal power dominated transportation there was no safe way
to cross east-west in the middle of the range, only nearer its
extremes save for the presence of a few rough passages opened
mid-range during the colonial era such as Braddock's Road and
Forbes Road, later improved into America's first National Roads
(respectively Cumberland Road, Lincoln Highway or designated U.S
40 and U.S. 30 in later