The memo on security threats to the national monument also said the ranger force is inadequate to protect visitors and the sculpture, USA Today reported Thursday.
The security review by the U.S. Park Service's Midwest staff began after environmental activists hung a protest banner July 8 on the monument that features 60-foot-tall sculptures of past presidents. The activists breached security and accessed anchors normally used by the National Park Service for periodic cleaning.
"It concerns me that information about secure areas of Mount Rushmore was inadvertently put out in the public sphere and used by Greenpeace," U.S. Rep. Stephanie Herseth Sandlin, D-S.D., said in a statement. "Going forward, it's critical for the safety of the monument that anyone who accesses these secure areas of the park understands the sensitive nature of the area."
Hundreds of people have been allowed in the secured areas for activities such as taking in views from the presidential pates, said Hugh Dougher, regional chief ranger in the National Park Service's Midwest office in Omaha.
The report said the Park Service and the Justice Department will look into beefing up criminal penalties for climbing Mount Rushmore.