Desert Rangers

The Desert Rangers were a group of survivalists and vigilantes living in the Nevada area, but who have also been found in Zion Canyon and Arizona. As of 2271, the Desert Rangers have merged with the New California Republic Rangers to form one cohesive group.

Background
The Rangers hail from the badlands of Nevada, from survivor communities that survived the nuclear devastation relatively unscathed. They trace their heritage all the way back to the Texas Rangers, who inspired their mission to make the wasteland better, one step at a time. To this end, they learn survival and combat skills before taking to the road to carry out their mission.

For years, the Rangers continued their efforts to protect the people of the wasteland against its hazards, from raiders to violent tribes. They eventually met their match when they clashed with Caesar's Legion in Arizona. The war went badly for the Rangers, who found themselves substantially outnumbered by Caesar's armies. Despite their superior training and equipment, the Rangers' numbers quickly dwindled. They were pushed out of Arizona and forced to call on the New California Republic for help which resulted in the signing of the Ranger Unification Treaty in 2271. In exchange for the NCR's protection of Hoover Dam, New Vegas and southern Nevada against the forces of the Legion, the Desert Rangers would be absorbed by the New California Republic Rangers. A special monument outside the Mojave Outpost commemorates the signing of the treaty.

Appearances
In Fallout, Tycho mentions that his grandfather was a Desert Ranger, and that his grandfather taught him and his father those survival skills. Tycho is also described to be wearing the Desert Ranger armor, however his model is not designed after it and is simply shown as wearing leather armor.

In Fallout: New Vegas, there is a monument at the entrance of the "Mojave Outpost" that depicts a Desert Ranger and NCR Ranger shaking hands, representing the pact between the two factions. NCR Veteran Rangers bear a nearly identical appearance to Desert Rangers.

They are also mentioned in the expansion for the Fallout board game, New California.

Behind the scenes
The Desert Rangers are a reference to Wasteland, the 1987 game to which Fallout is considered to be the spiritual successor. That game also featured Desert Rangers facing challenges in a post-apocalyptic setting (specifically, the American Southwest).