The large Ohio River valley area which Virginians called the District of West Augusta (the first county organized west of the Appalachian Mountains) sent two delegates to the Virginia convention in 1775, which eventually established the Commonwealth of Virginia. The District was governed from Fort Dunmore (as Virginians renamed it by 1774, and which later became Pittsburgh, Pennsylvania). In 1776, the Virginia General Assembly created the counties of Ohio, Monongalia and Yohogania from what had been the District of West Augusta. The Commonwealth of Pennsylvania also claimed much of this area, and established Westmoreland County with similar boundaries. Pennsylvania divided the area of Westmoreland County that Virginia considered Yohogania County into Fayette and Washington Counties in 1781 and 1783. It also negotiated its border with Maryland, and only ceded the area south of the Mason–Dixon line to the United States in 1787, when Virginia ceded its claims north of the Ohio River as well, allowing the Continental Congress to establish the Northwest Territory from the area west of both states' reduced claims.