The murder of Englishman John H. Tunstall on 18 Feb 1878 ignited the so-called Lincoln County War, during which an obscure young ranch-hand named Henry McCarty, alias William H. Bonney, would become famous in newspaper reports as "Billy the Kid".
This marker isn't at the actual murder site but is located on highway 70 below the hills where the event took place. Text of the sign:
John H. Tunstall Murder Site
In one of the Lincoln County War's most violent encounters, John H. Tunstall was shot and killed at a nearby site on February 18, 1878. Tunstall's death set off a series of violent reprisals between his friends, among whom was William "Billy the Kid" Bonney, and forces of the Murphy/Dolan faction of this tragic conflict. Tunstall, an English businessman, came to New Mexico in 1876.