Crews at Mount Rushmore are doing their annual maintenance on the carvings of George Washington, Thomas Jefferson, Abraham Lincoln and Teddy Roosevelt.
A team of workers is repairing sections of waterproof tarping at Mount Rushmore.
Cracks are also being repaired before winter to prevent water from damaging the sculptures when snow melts in the spring.
The maintenance will last through the end of the week.
"What they're doing is going through some of the original cracks and original patching material that is up here checking to see if there are any imperfections or flaws in that material or patching material that would allow water to go into the top of the heads and going through prepping those areas and then re-caulking them to keep the water out," said Rope Access Team Member Don Hart.
Mount Rushmore was designed by sculptor Gutzon Borglum, who, along with 350 workers, began making the presidents' busts in 1927.
Borglum died 14 years later in the spring of 1941 - seven months before the monument was finished, with his son overseeing the final work.