- “OPERATION RENAISSANCE II [CLASSIFIED]
Your orders are as follows.
Escort the Tribals west, to the Sierra Madre. [...]”
- —Military Orders
The Sierra Madre is an old-world resort and casino. Long the subject of wasteland urban legend, it was commonly believed to be a mythical construct until fairly recently.
The Sierra Madre is the subject of innumerable wasteland tall tales, a fabled city of gold where foolhardy treasure-seekers went, and never returned. In actuality, the Sierra Madre is just another old world resort, albeit an extremely luxurious one. Surrounded by a toxic red cloud, the casino and outlying villa are home to the original generation of Ghost People, former contractors trapped in their hazmat suits and mutated by the cloud. In the last years of the Mojave Wasteland, the Sierra Madre captured the imagination of a disgraced Brotherhood of Steel Elder named Elijah. Armed with the most unethical science the Old World had at its disposal, Elijah set about trying to unlock its secrets, using kidnapped scavvers fitted with bomb collars to try and break into the casino for him. Eventually, one such team apparently succeeded, though only one survivor made it back to tell the story. Elijah, however, was left alone among the ghosts, unable to let go of the desperation that drove him to the Sierra Madre.
Following its victory over Caesar's Legion, the NCR was eager to consolidate its gains. Knowing that the Sierra Madre was more than just a waster myth but also aware of the very real danger the location posed to explorers, the leadership made overtures to the residual Legion tribes to extract tech from the villa for them, in an effort to kill two birds with one stone. While initially unwilling, the tribals were eventually coerced with promises of anything they might want. With each subsequent visit, the tribals went further and further into the Madre recovering more old-world tech for the NCR who eventually gave them free reign over scavenging operations with no oversight, leaving NCR personnel stationed outside the gate.
Unbeknownst to the NCR, the tribals still harbored a deep antipathy towards them for the destruction of the Legion, a fact not lost on Elijah, who still remained at the Madre and had his own scores to settle. As the tribal expeditions were given more free reign, Elijah began making subtle overtures to them, first by leaving choice bits of tech out for them and eventually through direct communication. The tribals, resentful of being servants of the NCR, responded favorably and began taking direction from him, passing on tech of his choosing to the NCR garrison for transfer back to the Mojave wasteland.
In time, Elijah was able to achieve a long time dream of his through the tribals. A weaponized version of the blood-red cloud which surrounded the Sierra Madre was passed to the NCR sight unseen. His goal realized, Elijah instigated the tribals to take revenge against the NCR for the fate of the legion. The tribals, now known as "Cloud Walkers" by this time, had come to revere Elijah on the same order that they had Caesar, and they gladly obliged him. In the fighting, the NCR's officers were killed by rioting tribals and the retreating garrison blew the Sierra Madre gate to cover their retreat. In the aftermath, Elijah gave a glowing sermon, commending his children for giving the Bear-men the means of their own destruction. As the flag of the Legion was raised over the Sierra Madre's fountain, Elijah encouraged the Cloud Walkers to drink deeply to their victory and the bright future that awaited them.
None of them, including Elijah, ever left the fountain.
The Sierra Madre is only accessible by way of the Camp McCarran vertibird. Due to heavy concentrations of cloud residue in the area, the vertibird will crash land in the Madre's villa just outside the police station, alerting nearby Ghost people. Near the landing zone is a locked manhole cover to the sewers below. Short of a few buildings, most of the Madre's villa is inaccessible. Fighting your way through the Ghosts, a Survivor will eventually come upon the macabre remains of Elijah's final sermon. Searching his body reveals the sewer key as well as a transcript of his final words to his tribal followers. Through the sewers is Camp Adytum, a Followers safe zone.
- The location of the Sierra Madre in DUST is implied to be in the vicinity of Los Angeles, near the real-world city of Sierra Madre. This contradicts its description in Fallout: New Vegas as being in an isolated region of the Mojave desert, within a day's travel of Nelson, Nevada.