Mt. Rushmore (IMAGE) U.S. National Science Foundation Caption Mt. Rushmore granite crystallized from magma that formed 1.7 billion years ago. Credit Peter Nabelek, University of Missouri 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.