The Treaty of Lost Hills was a treaty ending the NCR-Brotherhood War on November 22nd, 2281 and set guidelines dictating the control of technology in the Mojave Wasteland, as well as stipulating the return of certain captured assets to the other party and limiting armaments to maintain the balance of power between the to parties.
While the Brotherhood of Steel, with their superior technology, were originally successful in their war against the New California Republic, the NCR quickly gained the upper hand with their superior numbers. The masses of NCR infantry, backed up by smaller numbers of tanks, artillery, and aircraft eventually managed to push the Brotherhood back to the are surrounding their bunker in Lost Hills, in the State of Maxson, in the NCR. The NCR military, however, could not pierce the bunker, which was hardened against conventional "bunker buster" bombs and other munitions, and the NCR were not willing to use the nuclear weapons they inherited from the pre-war US military. Instead, the NCR military blockaded the area surrounding the bunker, preventing food or supplies from flowing into the area, while regularly using their air forces to bomb Brotherhood surface installation and troops, as well as . Under increasing pressure from the NCR and influenced by a treaty with the Mojave Brotherhood in July, 2281, the Brotherhood cracked down and agreed to talks with the NCR on November 22nd, 2281 and the Brotherhood agreed to a ceasefire and began negotiations shortly afterwards.
- The Brotherhood of Steel will retain control over the former NCR State of Maxson and their Lost Hills bunker
- Any power armor or other Brotherhood of Steel assets captured by the NCR in the war are to be returned. The NCR is permitted to retain any power captured from the Enclave or scavenged from pre-war military bases. The Brotherhood is to return any gold assets seized in the attack on Redding.
- Any unclaimed technological artifacts in the territory of the NCR or Brotherhood may be claimed by the respective faction. Neither faction is to attempt to seize technological artifacts from the other or their citizens. Small technological artifacts- such as handheld energy weapons and terminals, are not to be seized from civilians or merchants, though they may be purchased at fair price. Civilian owners of artifacts which may be seize (such as heavy military hardware) must be paid for any items seized.
- Neither faction is to impede to movement of civilians travelers or merchants into, out of, or within their territory. Brotherhood forces moving through NCR territory from Maxson to Brotherhood holdings elsewhere must inform the NCR 24 hours before entering NCR land, waters, or airspace.
- Both parties are limited to five active (defined as mounted on a missile or based at an airbase) strategic (100 kilotons or greater) nuclear weapons, and five in reserve for the purposes of a deterrent. Tactical nuclear weapons of between 20 tons and 1 kiloton yield are limited to 50 warheads per faction. All other nuclear weapons are to be disarmed under joint NCR and Brotherhood oversight.
- The Brotherhood will retain control over the "Highwater-Trousers" TOSS-74 satellite weapons system (controls recovered by the Brotherhood in the Capital Wasteland), and the NCR will retain control over the HELIOS One satellite weapons system. Controls to all other satellite weapons systems are to be destroyed under joint NCR-Brotherhood oversight.
- Neither party is to maintain stockpiles of any strain of the Forced Evolutionary Virus.
The Treaty of Lost Hills played a major role in NCR Arizona Offensive. With hostilities with the Brotherhood ended, the NCR could focus their deadliest weapons, including their artillery, armored, and air forces against the menace of Caesar's Legion in Arizona. These weapons allowed the NCR to win a string of victories against the poorly armed Legion, capturing the major Legion-controlled cities of Nova Roma (Flagstaff), Phoenix, and Two Sun. This forced the remnants of the Legion to flee the NCR, as well as from insurgencies and slave rebellions who took advantage of the destruction of the Legion command structure to free themselves and retake their old lands.
The return of the gold reserves captured at Redding also helped bolster the NCR economy and return value to its currency, however, as much of the gold was destroyed in the battle, the NCR could not recover to pre-conflict levels with the gold alone. Fortunately, reserves of precious minerals found in Arizona, as well as increased industrial development in the Republic eventually allowed the NCR to reach new heights of economic power by 2300.
With the end of hostilities in the West, communications were opened up between the West and East Coast chapters for the Brotherhood of Steel. In the coming decade, the Brotherhood would transfer many of its assets to the east, where they faced no real organized opposition to their expansion. In 2287, many Brotherhood troops transferred from the West Coast would participate in their campaign against the Institute in the Commonwealth.