Which preposition to use with alleghany

for Occurrences 1%

A big band of warriors spread up and down the Alleghany for about forty miles, and on the 9th of February attacked all the outlying settlements.

in Occurrences 1%

"'Wal, we came down the Alleghany in two canoes, and shantied on the Ohio, just below where the Alleghany empties itself into it.

Which preposition to use with  alleghany