Mammoth Spring State Park [AR]
Mammoth Spring, the 10th largest spring in the world, and a National Natural Landmark, flows nine million gallons of water each hour. Following the Civil War, this immense water source attracted industrialists who built a gristmill, and later, a dam here. Next, the investors opened large roller mills and a shoe factory. Soon after, the railroad arrived. Still standing near the spring is the charming 1886 Frisco Depot. At the dam, you can walk through the 1925 power plant that brought electricity to the region long before most other rural areas.
The site offers short films, exhibits, tours, and occasional recreational and educational events.