Lost Hills was a pre-war government security bunker. Located almost entirely underground, the only indication of the presence of this installation was a small, reinforced structure containing the primary access elevator. After the Brotherhood seized the location, two sentries in powered armor stood guard at the entrance at all times.
The game takes place in the year 2161 on the West Coast of what used to be the United States of America, particularly in California. It begins in Vault 13, the protagonist's home. Vault 13's water chip, a computer chip responsible for the water recycling and pumping machinery, has broken. Armed with a PIPBoy 2000 and meager equipment, the protagonist is sent out into the remains of California to find another water chip.