Twin Tiers in the context of "42nd parallel north"

The Southern Tier is a geographic subregion of the broader upstate region of New York State, geographically situated along or very near the state border with Pennsylvania. Definitions of the region vary widely, but generally encompass counties surrounding the Binghamton, Elmira-Corning, and Jamestown metropolitan areas, along with the land of the Seneca Nation. This region is adjacent to the Northern Tier of Pennsylvania, and both these regions together are known as the Twin Tiers.

Geographically, most of the Southern Tier resides in the Allegheny Plateau of the Appalachian Mountains, with the eastern areas of the region nestled in the western portion of the Catskill Mountains. A longtime home of the Iroquois Confederacy, European settlers moved to the region after the American Revolutionary War. The fertile yet hilly land, combined with sweeping river valleys, led the region to support a combination of manufacturing industries (including large companies such as IBM and Corning Inc.) and farming, but with less development compared to neighboring subregions of upstate. Since the 1950s, the area is often considered to be a part of the Rust Belt, as manufacturing jobs have left the region.

The Genesee River (/ˌdʒɛnɪˈsiː/ JEH-nih-SEE) is a tributary of Lake Ontario flowing northward through the Twin Tiers of Pennsylvania and New York in the United States. The river contains several waterfalls in New York at Letchworth State Park and Rochester.

The river was historically used as a border between the lands of the Seneca to the east and the Erie and Wenro to the west. Later, the river provided the original power for the Rochester area's 19th century mills, and still provides hydroelectric power for downtown Rochester. Flooding occurred periodically in the river valley before construction of the Mount Morris Dam in the 1950s.