Updated

A man caught trying to climb Mount Rushmore National Memorial pleaded guilty to federal charges of trespass and failing to obey a lawful order, a prosecutor said Tuesday.

Patrick Marshall, 53, whose last known address is Chicago, was arrested by park rangers on Monday afternoon as he clambered on loose rock directly below the carvings of four presidents at the monument in western South Dakota.

Assistant U.S. Attorney Mark Salter said Marshall pleaded guilty to the charges Tuesday. A federal magistrate fined Marshall $500 and ordered him to pay $50 in court costs, Salter said.

"At no time during the incident was the sculpture or the visitors at Mount Rushmore National Memorial in any danger," Mount Rushmore spokeswoman Maureen McGee-Ballinger said.

McGee-Ballinger said she had no information on why Marshall wanted to climb the mountain, but she said such incidents occur several times a year.

"People are drawn for unknown reasons to disregard the regulations and climb up the sculpture," she said.

About 3 million people a year visit the memorial, which features the images of George Washington, Thomas Jefferson, Abraham Lincoln and Theodore Roosevelt carved into a mountain in the Black Hills.

McGee-Ballinger declined to comment on whether security upgrades put in place a few years ago helped detect the man.

A small group of Greenpeace members climbed the back of the sculpture and unfurled a protest banner over the front near Lincoln's face on July 8, 2009. After that, the National Park Service improved security at the memorial. Park Service officials said some security cameras and sensors were shut off or not working properly when the Greenpeace breach occurred.

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Information from: Rapid City Journal, http://www.rapidcityjournal.com

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Information from: Rapid City Journal, http://www.rapidcityjournal.com