Gutzon Borglum was the sculptor and was involved with the KKK. He was chosen because he was the sculptor of the "Shrine to the Confederacy” which was the inspiration for Mount Rushmore.
Guess it shouldn’t be too surprising given the way the land was taken from the local tribes despite it being sacred.
Credit to this comment by u/alcoholicorn that drove me to look it up.
[off topic]
‘Black Hills’ by Dan Simmons. Cool little novel about a Native working on the construction of Mt. Rushmore.