The Collaborative International Dictionary of English v.0.48:

Alleghenian \Al`le*ghe"ni*an\, a. Also Alleghanian
\Al`le*gha"ni*an\ (Biogeography)
   Pertaining to or designating the humid division of the
   Transition zone extending across the northern United States
   from New England to eastern Dakota, and including also most
   of Pennsylvania and the mountainous region as far south as
   northern Georgia.
   [Webster 1913 Suppl.] Allegheny