There’s nothing like a good mystery. 

If you or I were out walking in the Rockies we’d probably barely notice the different types of rocks under our feet, let alone realise that some rocks are a little out of place. 

But when John Craddock and his team of archaeologists found some unusual rocks at their feet they knew something was afoot.

Dr John Craddock is Professor in the Geology department at Macalester College, Minnesota