This project didn’t take place in one go. It was done step by step. The first phase which is completed was of George Washington in 1934. Thomas Jeffersons face was completed by 1936. Face of Abraham Lincoln and Theodore Roosevelt was finished in 1937 in 1939 respectively.
Along with these faces something else was being completed.
Gutzon Borglum was working on a secret project. He was waiting for Mount Rushmore to be completed so that he can add his secret project to it. Anyone know what he was secretly working on. He was waiting for right time for history to be revealed.