Today’s Wonder of the Day was inspired by Autumn. Autumn Wonders, “Who came up with the idea of carving the presidents' heads into Mt. Rushmore? ” Thanks for WONDERing with us, Autumn!

In honor of four particular former presidents, we're going to take a look at one of the most famous presidential memorials in America. And believe us when we say these guys are rock stars!

What are we talking about? Mount Rushmore, of course! Mount Rushmore National Memorial features the faces of four former presidents — George Washington, Thomas Jefferson, Theodore Roosevelt, and Abraham Lincolncarved into Mount Rushmore in the Black Hills region of South Dakota.

Doane Robinson, a historian from South Dakota, came up with the idea of carving the faces of famous people into mountains in the Black Hills as a way to encourage tourists to visit South Dakota. He enlisted Danish-American sculptor Gutzon Borglum to help him find the perfect spot.

Borglum and Robinson eventually settled on Mount Rushmore for several reasons. It's the tallest mountain in the area at 5,725 feet above sea level. It also faces southeast, which meant that the work would receive sunlight for most of the day.

Mount Rushmore is also made up of smooth granite. This durable rock is especially good for sculpting, because it erodes at a rate of only one inch every 10,000 years.

Rather than simply carving “famous people" into Mount Rushmore, Borglum thought the sculpture should have a patriotic, national focus. His idea was to carve the likenesses of four presidents who best represented the first 150 years of United States history.

Borglum chose George Washington because, as the first president, he represents the birth of America. Jefferson, who was responsible for the Louisiana Purchase, promoted the expansion of the nation. Lincoln, through his guidance through the Civil War, symbolizes the preservation of the country. Roosevelt, who encouraged construction of the Panama Canal, embodies the development of America.

The sculpting of Mount Rushmore began in 1927. With the help of over 400 workers, Borglum completed the 60-foot sculptures of the presidents' faces between 1934 and 1939.

Originally, construction plans called for each president to be sculpted from head to waist. When Borglum died in March 1941, his son, Lincoln, took over. Unfortunately, funding for the project ran out and construction ended in October 1941.

The entire project cost just under $1 million. Despite the size of the project and the dangers inherent in sculpting the side of a granite mountain, there were no fatal accidents during the project. Today, regular maintenance of the memorial requires mountain climbers to check for and seal cracks regularly.

Robinson's initial idea of attracting tourists has certainly come to pass. Mount Rushmore draws over two million visitors each year.

Wonder What's Next?

Join us tomorrow for a Wonder of the Day that will have you jumping out of planes and putting out fires!