Mount Rushmore was named after Charles E. Rushmore. His letter to Doane Robinson below explains how this happened:
RUSHMORE, BISBEE & STERN
61 BROADWAY, NEW YORK
December 14, 1925
RE: RUSHMORE MOUNTAIN: OR RUSHMORE ROCK
My friend, Mr. Lawrence F. Abbott, of The Outlook, has handed to me your letter to of October 10, 1925, relating to the project of sculpting Rushmore Mountain, or Rushmore Rock, in the Black Hills of South Dakota; and, since then, I have seen a copy of your letter of November 28, 1925, to Mr. Julian Blount, of Redfield South Dakota, concerning the naming of the mountain.
No doubt it will interest you to have accurate data on that subject. In your letter to Mr. Blount you say: "Rushmore Rock was named for Mr. Rushmore, a lawyer of Philadelphia who was interested in the Etta Mine." I am the lawyer in question, though of New York City, and not of Philadelphia. Late in 1883 the discovery of tin in the Black Hills was brought to the attention of a group of gentlemen in New York City and excited their interest. I was a youthful attorney at the time, and was employed by these gentlemen early in 1884 to go to the Black Hills and secure options on the Etta mine, and other cassiterite locations. My mission required me to remain several weeks in the Hills, and to return there on two or three later occasions in that year and in 1885. Part of my time was spent among prospectors at Harney, and at a log cabin built in that neighborhood. In my life among these rough, but kindly, men I conformed to their ways, and, may I say it with becoming modesty, was in favor with them.
I was deeply impressed with the Hills, and particularly with a mountain of granite rock that rose above the neighboring peaks. On one occasion while looking from near its base, with almost awe, at this majestic pile, I asked of the men who were with me for its name. They said it had no name, but one of them spoke up and said "We will name it now, and name it Rushmore Peak." That was the origin of the name it bears, and, as I have been informed, it is called Rushmore Peak, Rushmore Mountain and also Rushmore Rock.
Some time after the incident above narrated I was told that the name and identification of the Rock, or Mountain, was recorded in the Land Office in Washington at the instance of some of the good friends referred to, but I have never sought to verify this feet.
As you well say in your letter to Mr. Abbott this Rock is unique and lends itself admirably to a national monument of the kind you have suggested. I trust you may succeed in carrying out the proposed design.
Very truly yours,
Charles Edward Rushmore
Hon. Doane Robinson,
Superintendent, Department of History
Pierre, South Dakota