A new ad from the Pew Environment Group taglined “Don’t Undermine the Grand Canyon” calls on President Barack Obama to extend a one-million-acre mining ban around Grand Canyon National Park for the next 20 years. Robert Redford Running this week in the New York Times (pdf) , the ad is signed by actors Robert Redford and Ed Norton, filmmaker Ken Burns, Phoenix Mayor Phil Gordon, Los Angeles Mayor Antonio Villaraigosa, former New Mexico Gov. Bill Richardson and Theodore Roosevelt IV, direct descendant of the president who helped found the national park system A moratorium on mining within a million acres of the iconic Grand Canyon was imposed by current Interior Secretary and former Colorado Sen.