Mariposa Military Base: Where the Brotherhood and the Super Mutants Began

Mariposa Military Base is a pre-war US Army facility in central California, built to test the Forced Evolutionary Virus on human beings. Two of Fallout's biggest stories start there. In October 2077 Captain Roger Maxson's mutiny at the base founded the Brotherhood of Steel. Decades later a doctor named Richard Grey fell into one of its vats and became the Master, who turned it into the factory for his super mutants. (Fallout)

Why was Mariposa built?#

Mariposa was built for one job: to take FEV from animals to humans. The base's computer, ZAX, sums up the project. FEV began as a defence against Chinese bioweapons, grew bigger and smarter test animals, and by 2077 was nearly complete. Wanting to test it on people, the military built a large facility at the Mariposa installation and carried on with what it called volunteer subjects from the military. (Fallout)

A researcher's log disk dated 7 January 2077 records the order to move all FEV research to Mariposa. The researcher asked for it to be noted that neither they nor their staff recommended human testing. The soldiers sent to guard the base weren't told what the research was. (Fallout)

Roger Maxson's mutiny#

Captain Roger Maxson's diary covers the base's last weeks before the war. By 10 October 2077 his men had discovered what the scientists were doing, the test subjects were military prisoners, and the colonel in command had locked himself in his office. On 12 October Maxson stopped a soldier from executing a scientist and ordered interrogations instead. (Fallout)

They went badly. On 13 October Maxson shot Chief Scientist Anderson, who kept saying his orders came from the government. On 15 October the colonel shot himself as Maxson's men broke down his door. The interrogations that followed all ended in executions. A scientist named Shellman held out longest, and her account of her orders was specific enough to worry him. (Fallout)

On 20 October Maxson radioed the outside world and declared his unit seceded from the union. "They remember Jefferson Davis. What will history say about me?" he wrote. The bombs fell three days later. On 27 October he led his soldiers and their families out of the base, south to the government bunker at Lost Hills, where they became the Brotherhood. (Fallout)

Fallout 76 adds a radio log from before the war in which Maxson tells his friend Elizabeth Taggerdy he'll fill her in on what he has learned at Mariposa. (Fallout 76)

How Mariposa made the Master#

The sealed base sat empty for decades, but its vats didn't. Mutated creatures spread from it into the wasteland and preyed on caravans, mostly in the northwest. Harold, a trader in the Hub, put together an expedition to find the source, led by the doctor Richard Grey. (Fallout)

The base's robots were still on guard, and the expedition lost people getting in. Grey and Harold reached the vats, where a robotic crane hit them. Harold woke up in the wasteland, mutating. Grey landed in the FEV. (Fallout)

Grey's audio diary on the vats control computer tells what happened next. He crawled out, absorbed the creatures around him, linked his mind to the base computer and started dipping wanderers who strayed inside. When he worked out that subjects with low radiation converted best, he started building an army, then left to find a bigger home. (Fallout)

Mariposa stayed his factory. A super mutant called the Lieutenant ran it in 2161 and called it "the great procreator". Since the mutants couldn't breed, he explains, the Unity had to turn humans into super mutants in the vats. (Fallout)

The Vault Dweller and Mariposa#

Destroying the vats is one of the Vault Dweller's two final goals in the original Fallout, along with killing the Master. Inside, they deal with the Lieutenant and set the base's self-destruct, wiping out the source of the super mutants. (Fallout)

Mariposa in Fallout 2#

The ruins return in Fallout 2. The Enclave dug its way back in with slave labour to recover FEV, which its scientists turned into a plague meant to kill everyone outside the Enclave. A holodisk outside the base records what came next: "As expected the worker population has mutated rapidly once exposed to the pure source." The Enclave evacuated and blew the entrance to seal the mutated workers inside. (Fallout 2)

The Chosen One can get back in by blasting through the rubble. Inside are dead Enclave soldiers, a new generation of mutants and their leader, Melchior, who summons creatures out of the leftover goo in the old vat room. (Fallout 2)

Mariposa in later games and the TV series#

Later games keep coming back to it. In Fallout 3 Harold remembers exploring a military base ("I think it was called Mariposa") and a friend being knocked into the green goo, and the Citadel's records on Roger Maxson mention it. A New Vegas loading screen traces the Mojave's super mutants to the Master's army and the Enclave's experiments at Mariposa. (Fallout 3; Fallout: New Vegas)

The TV series tells the founding story without naming the place. In season two, Elder Cleric Quintus tries to win other chapters over with Roger Maxson's story: "an ordinary captain was sent to a research center in California", saw experiments on human subjects, and shot the scientists. Quintus uses it to argue that the Brotherhood began as a rebellion. (Fallout, "The Profligate")