May 21, 2018, 2:50 p.m. by Catie Leary
Composed of loose, gravel-like sediment and averaging about 6 feet in height, the puzzling natural mounds are a surreal sight.
Earth Day ideas
April 23, 2009, 9:10 a.m.
Earth Day is April 22. MNN is full of ideas on how you can make a difference.