The Ridgers were a tribe which originated in the Grand Canyon.
Based in the Grand Canyon, they were at war with the Blackfoot tribe. The weakest of the Blackfoot's enemies, Caesar and the Blackfoots stormed the Ridger's strongholds and exterminated the entirety of their tribe. While for most assimilated tribes, the able-bodied men were enslaved to fight for Caesar, with the women and children of the tribe exterminated without prejudice, the Ridgers were an exception and were wiped out completely as an example.
The Ridgers are mentioned only in Fallout: New Vegas.