Butler Knob is a peak on the Jacks Mountain ridge in south-central Pennsylvania within Rothrock State Forest. Its summit, reached by a rough road, is underlain by weather-resistant quartzite of the Tuscarora Formation from the Silurian Age, a geology that helps give the ridge its rugged character. A closed fire tower on the summit now supports a weather station that provides current forecasts for the area. Nearby, a scree slope offers broader views east, south, and west, with distant sightlines that can include Big Mountain, Sideling Hill, Williamsburg Mountain, and Blue Knob. Camping and other activities there are governed by Rothrock State Forest regulations.