Mammoth Spring is a large, first magnitude karst spring that arises in the Ozark Plateau within the state of Arkansas. It is the largest spring in Arkansas and the third-largest spring within the Ozark Plateau region behind Big Spring and Greer Spring. Mammoth Spring is the seventh-largest natural spring in the world.
The spring's outlet pool is contained entirely within Mammoth Spring State Park. The park is located in the town of Mammoth Spring, which lies in extreme north-central Arkansas. The outlet pool is adjacent to US Highway 63, only 500 ft. south of the Missouri border, and it can be readily seen from the highway.
Wikipedia https://en.wikipedia.org/wiki/Mammoth_Spring
Address 72554, United States
Coordinates 36°29'47.524" N -91°32'4.452" E