What was the westernmost point of the original 13 states?

The westernmost point of the original 13 states was the crest of the Appalachian Mountains, which formed the natural and politically significant boundary of British colonial settlement until the Treaty of Paris of September 3, 1783 transferred the territory between the Appalachians and the Mississippi River from Britain to the new United States. The Appalachian range runs about 1,500 miles from Alabama to Maine and varies from 70 to 300 miles wide. Crossing the range was difficult due to the mountainous terrain, dense forests, hostile relations with Native nations beyond the line, and limited road infrastructure.

The Royal Proclamation of October 7, 1763, issued by King George III after the British victory in the French and Indian War, formally prohibited British colonial settlement west of a line running along the crest of the Appalachians. The proclamation was intended to keep peace with Native nations, particularly with Pontiac's Confederacy that had launched a major uprising against British forts in 1763. Colonists generally ignored the line, and Daniel Boone led settlers through the Cumberland Gap into Kentucky in 1775.

By the time the colonies declared independence in 1776, frontier settlement extended west of the Appalachian crest in many places, particularly in western Virginia, the Watauga Settlements (now eastern Tennessee), and Kentucky. The Treaty of Paris of 1783 ending the Revolutionary War transferred the territory between the Appalachians and the Mississippi River to the new United States, including the Northwest Territory north of the Ohio River and the Southwest Territory south of the Ohio River. The Northwest Ordinance of July 13, 1787 organized the lands north of the Ohio River, prohibited slavery there, and established the procedure for admitting new states.

Kentucky became the 15th state on June 1, 1792, and Tennessee the 16th on June 1, 1796, the first new states formed entirely from territory west of the Appalachian crest. Specific subranges of the Appalachians along the colonial frontier included the Catskill Mountains in New York; the Blue Ridge Mountains in Virginia, the Carolinas, and Georgia; the Allegheny Mountains in Pennsylvania, Maryland, and West Virginia; the Cumberland Mountains in Tennessee and Kentucky; and the Smoky Mountains on the Tennessee-North Carolina border.

Cumberland Gap, where the Cumberlands meet the Blue Ridge in modern Virginia, Kentucky, and Tennessee, was the most important pass for early westward migration, used by perhaps 200,000 to 300,000 settlers between 1775 and 1810. The Appalachian frontier shaped American culture for generations through Scots-Irish settlement, Scotch-Irish folk traditions, regional dialects, and the development of distinctive Appalachian communities.