How Long Will Mount Rushmore Last? Geologists Have an Answer

Starting in 1927 and finishing in 1941, a team led by sculptor Gutzon Borglum turned the face of a South Dakota mountain into a monument to four of the greatest presidents of the United States.

Known today as Mount Rushmore, the four 60-foot-tall heads of George Washington, Thomas Jefferson, Theodore Roosevelt, and Abraham Lincoln look out over the Black Hills of South Dakota from their rocky perch.

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Before Europeans arrived, the indigenous Lakota people called the mountain "Six Grandfathers" in honor of their ancestors and the 'six directions.'

During the Black Hills gold rush, in 1884 and 1885, New York attorney Charles E. Rushmore visited the Black Hills to check on his company's land holdings in the area. He saw the future Mt. Rushmore and asked his guide what the mountain's name was. The guide said it didn't have a name and suggested it be called 'Rushmore.' It was officially recognized as Mount Rushmore in 1930.

The mountain is made of granite formed from volcanic activity about a billion years ago. Granite is a very hard rock. While nothing will last forever, a sculpture carved from the granite of the Black Hills will last a long time. But, how long?

The rock is very resistant to the ravages of wind and water. According to geologists, granite erodes about one inch every 10,000 years. Being carved out of solid granite, it will take nearly two and a half million years for just the 240-inch-long noses on the faces to wear away.

If your descendants make a trek to the Black Hills in 500,000 years, they will likely see that the faces have lost some of their definition. But your 20,000th-great-grandchild will still be able to recognize George, Abe, Tom, and Teddy.

If wind and water erosion don't lead to the faces falling off in a rockslide, they will probably last upwards of seven million years.

Officials take measures to keep the faces from falling apart. They monitor hairline cracks and use thousands of feet of fiber optic cable to reinforce problem areas.