Devil's Lake formed about 14,000 years ago as the last glacier in the area retreated, leaving glacial debris that plugged both ends of the gorge and diverted an ancient river, so that a lake remained behind. The first inhabitants arrived during the glacier's final retreat, and Native Americans lived in the area for 500 generations before the first recorded white visitor, John T. de La Ronde, arrived in 1832. They believed a good spirit, or Manitou, lived in the depths of the lake and called it Spirit Lake or Sacred Lake. Between 700 and 1100 AD, a Middle-Woodland Native American culture known as the Effigy Mound Builders constructed earthen mounds in animal shapes near the lake, and the mounds still exist. After de La Ronde's visit, European-descended settlers were drawn by stories of the purple bluffs rising 500 feet above the water, and they brought customs of land ownership and fencing as well as superstitions about spirits in nature. Echoing noises from the bluffs added to the gorge's mystical aura, and settlers, thinking in terms of evil spirits, changed the name from Spirit Lake to Devil's Lake. In 1911, Devil's Lake became Wisconsin's third State Park.