Secrets of the Underground — Season 1, Episode 4: Rocky Mountain Monsters

Episode synopsis

Rob Nelson examines a set of bizarre markings that suggest a violent clash between prehistoric beasts. In California, he investigates if a strange lake is a home to alien life.

About Secrets of the Underground

A search for an underground escape route said to have been used by Al Capone. Also: who or what built earthen mounds in Washington state.

More episodes from Season 1

• E1Capone's Escape Tunnels
• E2Mystery of the Serpent Mound
• E3America's Buried Massacre
• E5Great Lakes Bermuda Triangle
• E6California's Hidden Doomsday
• E7Secret History of the New World
• E8American Stonehenge