Samuel Langhorne Clemens first used this pen name in 1863 while with the Territorial Enterprise in Virginia City, Nev.
It was there he first adopted the pen name "Mark Twain" on February 3, 
1863, when he... [DOC] [TLE] Mark Twain Museum - Virginia City - Basement of the Territorial ... [PAR] Mark Twin Museum in Virginia City Nevada, Where Samuel Clemens Became 
Mark Twain at the Territorial Enterprise Newspaper.