SIOUX FALLS, S.D. (AP) — A historian thought gigantic sculptures of significant Western figures might bring more people to the Black Hills of South Dakota and ran it by an artist in 1924.

Sculptor Gutzon Borglum told the historian to think bigger. Three years later, he began carving four presidents’ faces into the granite pinnacles.

October marks 75 years for the Mount Rushmore National Memorial, which is a muse for political cartoonists and makes frequent cameos in movies. It’s also a big draw for tourists, with about 3 million people visiting each year.

To celebrate the milestone, the National Park Service held events during the summer in connection with its own 100th birthday.