Mule Spring Rockshelter (IMAGE) Desert Research Institute Caption This is a photograph of the Mule Spring Rockshelter opening and apron as it appeared in 2016. Credit DRI Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.