And here’s one more: Those four presidential heads carved into a mountain in South Dakota are not naturally occurring.

It could have been carved into a different formation

It was the idea of South Dakota state historian Doane Robinson to carve faces of iconic historical figures into the side of a mountain in the Black Hills. His reason: to promote tourism into the then-seldom visited region. When he proposed the idea in the 1920s, Robinson initially planned for the project to happen at Needles, a series of jutting, naturally-forming granite columns in the Black Hills. His chief sculptor, Gutzon Borglum talked him out of it—he didn’t think the granite was of high quality enough to sustain the carving project. Furthermore, it was opposed by Native American groups. Instead, Robinson and Borglum settled on Mount Rushmore, which had good granite quality and faced east, ensuring maximum sunlight for workers. (That site was also in the Black Hills and was also adamantly opposed by Native American groups.)

It could have had a different series of four heads

Robinson had picked out four heroes of the West for depiction in giant sculpture on Mount Rushmore: Lewis and Clark, Buffalo Bill Cody, and Red Cloud, a leader of the Lakota who had lay claim to the Black Hills before it was taken over by the United States. Borglum thought four Western heroes was too specific and regional and talked Robinson into doing four American presidents instead: George Washington, Thomas Jefferson, Abraham Lincoln, and Theodore Roosevelt.

Its construction outlived its architects

Construction on Mount Rushmore—which at first was just lots and lots of dynamite blasts—began in 1927. The four faces of the presidents were slowly finished between the years of 1934 and 1939. Borglum died in 1941, forcing his son, Lincoln, to lead up the project. But that didn’t much matter—construction ended in October 1941 when the project ran out of money. (The U.S. entered World War II not long after, which likely would’ve ended construction on the site anyway.)

It was supposed to be bigger

What would Mount Rushmore have looked like if the original plans had been finished? Borglum had planned to depict not just the heads of the presidents, but all four down to the waist.

Additions have been suggested

In the decades since Mount Rushmore was completed, there have been many drives to add another important American to the monument. (And not just presidents: feminist activist Susan B. Anthony was bandied about as an addition in 1935.) Serious consideration has been given to adding Franklin Roosevelt, John F. Kennedy, and Dwight Eisenhower to Mount Rushmore. Grover Norquist, a major Republican strategist is also the chairman of the Reagan Legacy Project. That organization has aimed to get something in all 50 states named after President Ronald Reagan; it has also suggested adding Reagan to Mount Rushmore, or even removing Roosevelt in favor of Reagan.

It’s going to stay at four

Reagan or any other face probably won’t get added anytime soon, if at all: There isn’t any room. According to the National Park Service, when Borglum selected the site, he mapped it out for exactly four faces. There isn’t much additional room to work with, and what is there doesn’t have very workable granite.