Conquest of the Allegheny Mountains in Pennsylvania: The engineering geology of Forbes Road: 1758-1764

By the mid-1700s, the parts of British colonies along the eastern seaboard of North America were settled, safe and civilized. This was by no means the case not very far inland in the Allegheny Mountains and at The Forks of Th e Ohio, now the site of Pittsburgh, from which the Ohio River flows west. V irginia claimed The Forks but was driven out by the French. In 1754, Lieute nant Colonel George Washington of the Virginia Militia tried and failed to reverse this, bringing on the French-British Seven Years War, the French an d Indian War of American history. A second British attempt in 1755 via Wash ington's route, Virginia, Maryland and to The Forks, was crushed. In 1758, the invalid General Sir John Forbes was ordered to try again. He concluded to go from Carlisle, Pennsylvania to The Forks as directly as possible. The re was no through road, but in five months his 6,000-man army, managed for Forbes by Colonel Henry Bouquet, cut a road capable of carrying wagons and artillery through the mountainous, heavily forested Alleghenies. Late in th e year the outnumbered French abandoned The Forks and retreated to Canada. This paper examines the setting of the 217 mi of Forbes Road and the physic al obstacles facing Forbes' army. Adding only the most significant climbs a nd descents, construction of Forbes Road was the equivalent of conquering a single obstacle more than 8,000 ft high, something that might have given e ven Hannibal pause. It was a remarkable job, done with very few of the tool s we now have.