About 20,000 years ago, a powerful, whirling mixture of frigid glacial water, sand, and stones wore away solid rock and formed this glacial pothole. At its discovery, geologists proposed that it was carved by a waterfall falling through a crevasse in the glacier, and many modern geologists still support that original theory, with a recent addition placing a lake on top of the glacier as a long-term water supply for the waterfall. Other geologists argue that there was no waterfall and that a large, fast-moving stream under the glacier supplied the swirling water. Melted ice carrying abrasive sand and stones created a world-class glacial pothole that measures 38 feet from bottom to top and, at one place, is 42 by 24 feet in diameter.