At the Pennsylvania state line in South Valley, PA 346 exits the Allegheny National Forest and becomes NY 280 upon entering New York.

Here, NY 280 turns north, traversing a small waterway separating Quaker Lake from the reservoir before reentering the Allegany Indian Reservation limits.

[3] Families living in the hamlet of Cold Spring were brought in through the Cornplanter Grant in the early 1800s, and by 1809, the village located along future–NY 280 exceeded 500 people in log houses.

The designation ended in Quaker Bridge, a community situated on the eastern riverbank near the modern junction of NY 280 and Allegany State Park Route 3 in the town of Elko.

Much of NY 280 was inundated by the new reservoir, as were Cold Spring, Quaker Bridge, and a significant portion of Pennsylvania Route 346 (PA 346) that ran along the river in Warren County.

[10][11] NY 280 now began at the realigned PA 346 at the state line and ended at exit 18 of the Southern Tier Expressway, which was built between Steamburg and Salamanca during the mid-1960s.