Res

Res is a mentioned only location and language in the Fallout: New Vegas add-on Honest Hearts.

Background
Joshua Graham refers to the location as somewhere east of the Grand Canyon. He tells the Courier that he believes the Dead Horses tribe members were originally refugees from Res, and that their language is a combination of their own and that of travelers who were visiting when the Great War occurred.

Behind the scenes

 * Several Navajo words (e.g. yá'át'ééh, meaning "hello" in the Diné language) are spoken by some of the tribal members when greeting the player character.
 * Fallout: New Vegas project director Joshua Sawyer stated that Res was located east of the Grand Canyon and that the Dead Horses' language is based on German, English, and Navajo, a mixture of languages of those both living in and visiting Res when the Great War occurred.
 * It could likely be the refering to the Navajo Nation, the large reservation (or "res") in the northeastern corner of Arizona, east of the grand canyon.