Desert Rangers

Desert Rangers were a faction living east of California, in the Nevada area.

Background
They are descended from people who survived the devastation when the Great War happened, likely living among the badlands of Nevada. This small community kept a strong survivalist contingent -- so they still had some small arms and books. They probably had something like the cliff-dwelling Indians going on for their town. In early 22nd century, they clashed with a fat freak of a tribe leader in the ruins of Las Vegas.

When the Caesar's Legion was formed, the Rangers clashed with it out east. The war went poorly for them and eventually they found themselves losing it. That's when the NCR Rangers came in. In 2271 the Desert Rangers signed an agreement with the NCR to be amalgamated with the NCR Rangers in exchange for NCR's protection of the Hoover Dam and Nevada from the Legion.

A monument at the Mojave Outpost depicts this historic moment.

Tycho's answers

 * We Rangers hail from back east, what used to be called Nevada. Our heritage stretches back to the days of the Texas Rangers. We learn survival and combat skills in order to go out into the world and have a chance of surviving and making things better.
 * Had some pretty good training, and some good weapons, too. My grandfather was a Ranger way back when, and he taught my father everything he knew. Dad passed it on to me.

Appearances in games
In the first Fallout, Tycho mentions that his grandfather was a Desert Ranger, and that his grandfather taught him and his father those survival skills.

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 groups.

Behind the scenes
Tycho's grandfather was a Desert Ranger, a reference to Wasteland, the 1980s game which is considered to be Fallout's predecessor. That game also featured Desert Rangers facing challenges in a post-apocalyptic setting (specifically, the American Southwest).