Here is Hudson with Cretaceous sands on his face! Many mourn the fact that Colorado doesn't have an ocean, but it has an ancient one! At Marshall Mesa in south Boulder there is a rare outcropping of Fox Hills sandstone. This sandstone is soft and was the ancient beach of the Cretaceous Seaway. During this time mosasaurs swam along the shores and plesiosaurs, like Thalassomedon, walked its sands. The world here was tropical and huge swamps dominated the landscape. Over long periods of time, animals and plants sank beneath their own weight and formed large coal beds, called Pierre Shale, which is tucked beneath the Fox Hills sandstone. These tropical swamps are the reason why Marshall Mesa was an epicenter for coal mining. Now, my children play on these ancient shores and cyclists ride the flowstone with eagerness. As you ride don't ignore the tumultuous and beautiful world below you, before you.