Eureka ! Eureka ! is an and final in " " if the Courier sides with the NCR in 2281 . Description . Defend the Hoover Dam alongside the NCR from the invading Legion army . Detailed walkthrough . After completing You ' ll Know It When It Happens , at the very moment the Courier might choose to side with the NCR for the final battle ( thus completing For the Republic , Part 2 ) , the player character will be automatically taken from Col . Moore ' s office to General Oliver ' s compound , where the General will begin a briefing . The Courier is given the chance to wait , as this begins the end quest for the game . If the player chooses to continue , after the briefing , Legion members attack the Hoover Dam and you need to fight your way through the power plant rooms and head east toward their base . You will start in power plant 04 . Proceed to power plant 02 , then power plant 01 , dispatching Legion troops on your way . Climb the stairs on your left in power plant 01 , then proceed north along the balcony . Follow the passage along the left , then go up the stairs , and exit via the elevator to the Hoover Dam visitor center . At this point , you will begin to notice assistance appearing from companions and factions you have helped out along the way . Exit via the double doors on the east side to Hoover Dam . Proceed to the north along the curved walkway above the dam . There is a door hidden in the side of the dam that you can pick with a Lockpick skill of 75 ( hard ) . Enter the Hoover Dam checkpoint . From here , you can check the terminal ; if you have a Science skill of 100 and a , you may use the terminal to detonate one group of legions ( the blast is centered near the first tower ) . When you exit on the other side , you will encounter a squad of NCR Veteran Ranger s . Their commander will thank you for your support and ask you how to coordinate their assistance . The player can respond with several dialogue choices which lead to the following actions : After crossing the dam , head left along the bridge to the east , and continue , following the road . Enter the gate to the Legate ' s Camp . Head east into the camp , following the path up the side of the ridge . There , you will encounter Legate Lanius . Note that with a Speech or Barter skill of 100 , you can pass a series of skill checks , and avoid fighting him . The Legate is extremely challenging , and many Legionaries will come out and attack you . If you pass all of the previous speech checks and fail the last one , you get another Speech challenge [ 85 ] which can convince the Legate to fight you one on one - all the other Legion troops will become friendly to you . After either killing the Legate , or passing a series of speech checks to end the fight peacefully , you should notice the gate to the camp has closed . Head back to it . The gate will explode and you will meet with General Oliver . Behind the scenes . " Eureka " is the state motto of California . The word comes from the ancient Greek word , heúrēka , literally meaning " I have found " . There is a story of the famous Greek mathematician Archimedes , who shouted " Eureka ! " upon making a and ran naked through the streets of Syracuse .