Henry's Knob is a mountain and Superfund Alternative Site in York County South Carolina at 1,120 ft (340 m) above sea level. It is near the North Carolina border and the town of Clover, South Carolina. The mountain was the site of an open-pit kyanite mine, which was under operation from 1947 to 1970. At the time of its discovery, the deposit of kyanite on the mountain was the world's largest United States Environmental Protection Agency (EPA) testing has determined that approximately 450 residences in the vicinity relying on well water are affected by groundwater contamination from the former mine. The mountain was stripped of approximately 100 feet (30 m) due to the mining operations. Today, the site is overgrown, with many pits and waste ponds still evident.