Today's climb to the peak of Mount Rushmore isn't the first time Greenpeace has used the memorial as a grand stage for a public protest.

In October 1987, five activists from the organizations tried to place a banner shaped like a gas mask over George Washington's carved stone face, to protest acid rain. Authorities interrupted and arrested the activists before they finished unveiling the banner.

Security at the mountain has been of increasing concern to federal officials, particularly after the Sept. 11, 2001, terrorist attacks.

A 2005 Congressional report said security at Mount Rushmore remained "a major Park Service concern" despite beefed-up patrols and improvements, including security cameras, fences, gates and lights.

The report, "Homeland Security: Actions Needed to Better Protect National Icons and Federal Office Buildings from Terrorism," was produced for the House Committee on Government Reform. It noted several threats and incidents at the memorial before the Sept. 11, 2001, terrorist attacks.

• Between 1970 and 1973, members of the American Indian Movement made several attempts to occupy and deface the monument.
• In 1975, a bomb went off in front of the visitor center before visitors' morning arrival.
• In 1987, the environmental group Greenpeace climbed the mountain with plans to unfurl a 160-by-50-foot protest banner reading "We the people say no to acid rain" over the presidents' faces.
• In 1991, the Park Service received threats to assassinate then-President George H.W. Bush during a celebration marking the monument's 50th anniversary of completion.
• In 1999, a Colorado man was arrested for threatening to blow up the mountain.
• The incidents prompted the National Park Service to spend about $2.9 million on security measures to protect the monument.

After the 9/11 attacks, the National Park Service increased the park's law enforcement budget and adjusted its security focus to include protecting visitors and employees.

Mount Rushmore National Memorial covers 1,278 acres, 40 of which are part of a visitor service area with hiking trails, an amphitheater, museum and bookstore.

Contact Jeremy Fugleberg at 394-8421 or jeremy.fugleberg@rapidcityjournal.com

The Associated Press contributed to this report.