Q. Where is there evidence of volcanic activity in Arkansas? A. "Crater of Diamonds offers park visitors a one-of-a-kind experience—the adventure of hunting for real diamonds. You’ll search over a 37 ½-acre plowed field that is the eroded surface of the world's eighth largest diamond-bearing volcanic crater. If you find a diamond, it is yours to keep." -- http://www.craterofdiamondsstatepark.com/