This state park boasts the world's largest glacial pothole; 38 feet deep and up to 42 feet across. The pothole formed during the Wisconsin Glacial Period about 15,000 years ago.

A pothole usually is a hole which is worn into the bedrock of a stream at the base of waterfalls or in strong rapids. The moving water spins sand, gravel and rock fragments in any small indentation in the bedrock. After enough time, the sand and stones carve out an elliptical hole. Potholes may also form under or near the edge of glaciers by the action of glacial meltwater.

Archbald Pothole was discovered in 1884 by coal miner Patrick Mahon while extending a mineshaft. Mr. Mahon fired a blast of explosives and water and stones came rushing out. The miners fled fearing that the mountain was falling on them. Edward Jones, the manager of the mining company, investigated and ordered the area cleared of debris. 800 to 1000 tons of small rounded stones were removed and Mr. Jones realized that the vertical tunnel was a large pothole.