[ Register or Signin to view external links. ]
15 G

This mission is the final mission in the "Legion" chapter. When you talk to Caesar to complete "Render Unto Caesar" you will be prompted to go to the Hoover Dam. When you accept, you will be sent to Legate's Camp to start the mission. After talking to Legate Lenius, Move across the dam , fighting your way through to NCR opposition. Personally, I used the Sniper Rifle because the baddies around tended to drop them, and ammo for it as well. With about 20 Stim-Packs I made it through this entire mission no problem.
My method of doing this mission was going straight to General Oliver. To do this, when you cross the dam, go to the visitor's center, and follow the doors to "Hoover Dam 01", 02, 03, 04, and finally General Oliver's room.

Immediately* after you enter the room, you will begin a conversation with the General. Due to some unlucky chem addictions, I was unable to test if the "Speech - 100" option would have completed the mission there, but I assume that you ARE able to talk your way out of fighting him. I had 100 speech going into the Dam, but due to taking lots of chems, my speech was dropped to 98 and I had to chase him down to kill him.
*Note. There will be NO time for pip-boy-ing between the time you open the door and the time General Oliver begins talking to you. If you want to out-speech him and want to use a magazine to help, read it BEFORE you go through the door.

When he begins to run, you will need to head left up some stairs, and then into one of the side-rooms near the blue barrier. It has a generator in it which you can shoot to deactivate the barrier. Follow the barrier up the stairs and kill every NCR guy around. I found it easy to go straight upstairs, bringing with me most of the troops I was supposed to kill, then applying a frag grenade or two to the bunch and doing massive damage to everybody. Killing them, as well as General Oliver will complete the final bit of this quest, and when you backtrack through the Hoover Dam, you'll be intercepted by Legate Lenius who will congratulate you and thank you for whatever you've done, and the quest should complete, and achievement should unlock.

After all this, the "end-game" will occur, detailing most of the things you've done to impact different factions in the game, and is really quite neat.