Precipitation that falls in southern Missouri seeps into the water table and flows through a vast system of passages and cavities. These cavities form an underground river that ultimately emerges on the surface at the town of Mammoth Spring, Arkansas. The emerging water forms a 10-acre spring pool that drains over a high stone dam. The spring generates a harmonic mean flow of about 9 m³/s. The water emerges at a constant 14 °C. The spring itself cannot be viewed at the Mammoth Spring site because its mouth is more than 21 m below the surface of the large spring pool. Nine miles northwest of Mammoth Spring, visitors can see a portion of the underground river that feeds the spring at a collapsed cave inGrand Gulf State Park in Missouri. The remains of a portion of the cave are now a 40 m deep chasm with a natural bridge over it. Dye tests have proven that the water flowing through the 40 m chasm at Grand Gulf exits through the existing cave and emerges at Mammoth Spring.
Industrial use
The spring was used to power a gristmill from the times of the earliest European settlement. The Mammoth Spring Milling Company constructed a dam and a water-powered gristmill just downstream of the outlet of the spring lake. In 1925, the dam was purchased by the Arkansas-Missouri Power Company which constructed a hydroelectric plant at the dam. This plant supplied power to the surrounding area until 1972.
Park
In 1957, Mammoth Spring State Park was established. Surrounding land claims could not be acquired until 1972, however. Prior to 1972, the Mammoth Spring Cattle Sales Barn was co-owned and run by local entrepreneur Bert Kenneth Bishop and his associate, roughly on the site of where the Welcome Center now stands. Local farmers would routinely come to the site to sell livestock and other wares, such as Howard Green, who sold home-made walking sticks. Following this period in history, the State legislature voted to condemn the land and join the plot to the state park. The original Frisco Depot was restored in 1971 and now functions as a repository for artifacts and memorabilia related to the railroad and the spring area. The State Park provides a visitor's center, picnic areas, walking trails, and tour access to the dam and hydro plant. The United States Fish and Wildlife Service maintains a fish hatchery near the spring.
