During most of the Paleozoic Era, what became the Ouachita Mountains was the bottom of a shallow sea, where several sedimentary layers were created. About 500 million years ago a collision of the South American Plate with the North American Plate caused the shale and sandstone layers to fracture and fissure, creating mountains of the folded rocks. The thermal springs emerge from the plunging crest line of a large overturned anticline in the Zigzag Mountains of the Ouachita anticlinorium. The overturned anticline plunges toward the southwest into the Mazarn Basin. There are two recognized major thrust faults trending nearly parallel to fold axes that define the northern and southern limits of the thermal springs discharge area. The northern fault extends nearly parallel to Fountain Street northeastward about onto the southeast flank of North Mountain, and dips about 26 degrees north. At the northern extent of the thermal springs, this fault is suggested to form along the bedding contact of the Hot Springs Sandstone and Stanley Shale, with the Stanley Shale forming the hanging wall of the fault. The southern fault extends northeastward about roughly along the axis of the Hot Springs anticline, and dips about 44 degrees north. It has been proposed that a fault splits away from the southern fault, trends west and connects with the northern fault. A natural ravine trends along the location of this fault. Extensive cracks, joints, and fissures in the Bigfork Chert, Arkansas Novaculite, and the Hot Springs Sandstone allow the water to flow in the thermal springs area. Dissolved minerals in the water precipitate to form the white to tan travertine or "tufa rock" seen near the openings of the hot springs.