Mariposa Military base is a top secret science facility, built to house the F.E.V. after West Tek (now The Glow). It was constructed in October 2076, and one year later, Major Barnett had transferred all F.E.V. research over to it. Robert Spindel and Rodger Maxson (who created the Brotherhood of Steel after the great war) were given charge to the project but were horrified to find out that their scientist were using the F.E.V. on living test subjects. Spindel killed himself five days later. Giant vats of F.E.V. were created and human subjects were dipped in to see the effect of the virus on people and learn how to control it.
After the death of Spindel, Maxson took charge of the soldiers and interrogated Robert Anderson, chief scientist, and executed him shortly after. Maxson declared himself in charge of the base and deserting the army, but no reply came as all other soldiers were busy fighting with the Chinese. Three days later, the bombs dropped and the Great War ended two hours after it started.
Maxson and his soldiers survived the radiation within the base. Afterwards, they buried the dead, took the technology and weapon schematics with them and left for Lost Hills were they formed the Brotherhood of Steel.
Years later, an expedition led by Harold and Richard Grey, found Mariposa. This led to Richard Grey discovering the F.E.V. after him and his party battled with the robot defense systems of the base and took heavy casualties. Grey became very intelligent and within a few days, neurolinked himself to the computers and drew much information, forming this idea of 'Unity'.
Using the F.E.V. he created an army of Super Mutants. He entrusted the base to the Lieutenant (known as Lou Tenant by the other Super Mutants) and left to LA underground Vault to make himself a god figure.
The Vault Dweller eventually comes through in 2162 and destroys the base, blowing it up from within.
In 2236, the Enclave find the military base. In 2237 they pull out after some soldiers started to become infected with the virus. Frank Horrigan was one of those infected, growing to an abnormal size. After the Enclave left, some 2nd generations Super Mutants took it back over under the leadership of a Super Mutant named Melchior, who prided himself on his magician talents like he once had in life. Back then he could pull a rat out of a hat, now he pulls monsters out of radiated pits of goo.
In Spanish, Mariposa means 'Butterfly'. The name could be for two reasons:
-A butterfly is an evolved caterpillar as a Super Mutant is a better human.
-The butterfly effect. The two Fallout games, as well as every other one set in the same universe, seem to revolve around the Super Mutant threat.