GEOLOGIC CONSIDERATIONS RELEVANT TO FORT GRANVILLE (CENTRAL PENNSYLVANIA; FRENCH & INDIAN WAR)

Within the Appalachian Valley-&-Ridge Province, in a synclinorial valley underlain by Silurian shales, lay Fort Granville. Its probable site is 1.0 mi (1.6 km) W30ºS from the courthouse in downtown Lewistown (Mifflin County), 300 ft (100 m) NE from the intersection of Crystal Spring Avenue and Riverview Drive. The fort was apparently on the southwestern lip of the shallow ravine there cutting down into the north bank of the Juniata River. Grading for street and house construction since has disturbed the soil on the site so much that no clear-cut evidence remains of the fort.

Fort Granville was built at the end of 1755 as one of a chain of forts to protect the northwestern mountain frontier settlers from Indian raids, a morale boost, but military failure because the forts were too widely spaced, given travel conditions at the time. The site, on a wide valley floor between high ridges, takes advantage of a topographic constriction narrowing the valley (enhancing visibility of forces moving past), a location mid-way between two water gaps (a principal overland route through the moutain ridges), and situation on the bank of a major river (ready access back to settled areas to the southeast). The valley was heavily forested (providing logs for construction), with alluvial soils or soft shale bedrock (hence stockade post-holes easily dug). Water could be supplied from either the river or an on-site small spring (which, like most in the region, was seasonal and thus was dry when needed in the siege in mid-1756).

In summary, some of the characteristics of the Fort Granville site had positive military value, but about as many, in actual practice, turned out to be negative instead.