Dunes are sandy elevated landforms that typically have plants growing in them. They are often found along low-lying coastlines where strong waves and currents drive sand onshore to the beach.

Star dunes are common, but scientists have long wondered about their formation and puzzling absence in the geological record. Now, research has revealed new clues.

After that clay was formed, that’s when the sand dunes moved in around 3,500 years ago,” she said. To determine which sand is recent, scientists use optically stimulated luminescence.

Nathaniel Minor/CPR News Jason Loughrin and his children, Ian, Patrick and Claire, of Erie, Colorado, play in Medano Creek at the Great Sand Dunes National Park and Preserve on a hot morning June ...