Mammoth Spring is the largest spring in the US state of Arkansas. It is located in Mammoth Sring State Park, a state park of Arkansas, in the extreme north-central part of the state at the town of Mammoth Spring.

Mammoth Spring

Rainfall in southern Missouri seeps into the water table and flows through a vast system of passages and cavities. These cavities form a main channel and the groundwater reaches the surface at the town of Mammoth Spring, Arkansas. The emerging water forms a 10 acre (40,000 m²) spring pool that drains over a high stone dam and forms the headwater of the Spring River. The spring generates a flow of almost 10 m³/s (370 cubic feet per second). The water emerges at a constant 14 °C (58 °F). The spring itself cannot be viewed at the Mammoth Spring site because its mouth is more than 21 m (70 ft) below the surface of the great spring pool.

Local folklore claims that the spring first emerged when an Indian chief was digging the grave of his son who had beend killed while searching for water during a severe drought. Legend holds that the massive spring will flow forever because the young Indian brave had died while searching for water.

Nine miles northwest of Mammoth Spring visitors can see a portion of the underground river that feeds the spring at a collapsed cave at a Missouri State Park called Grand Gulf State Park . The remains of the cave are now a 40 m (130 ft) deep chasm with a natural bridge over it. Dye tests have proven that the water flowing through the 40 m (130 ft) chasm at Grand Gulf emerges at Mammoth Spring.

The spring was used to power a grist-mill from the times of the earliest settlers. The Mammoth Spring Milling Company constructed a dam and a water-powered grist-mill just below the site. 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.

In 1957, Mammoth Spring State Park was established.

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.