In 1970, the year that Earth Day was first celebrated, Robert Redford stands in a wintry landscape with the snowy mountains of Utah, the state he now calls home, as his backdrop. Since that time, Redford has been a tireless supporter of environmental causes, fighting to preserve America's natural beauty and resources. As Earth Day rolls around again (April 22), LIFE asked the filmmaker and activist to choose his favorite photos of Western landscapes, and to explain why it's so important we take steps now to protect them.