Climb Ev'ry Mountain

 is a side quest in Fallout: New Vegas.

Quick walkthrough
A sniper is killing NCR soldiers and civilian refugees in the Bitter Springs Refugee Camp. Captain Gilles wants you to track down this unknown assailant.

Quick Walkthrough

 * Head to Bitter Springs and speak to Captain Gilles located in the tent behind the infirmary, follow the dialogue asking about Bitter Springs with her to begin the quest.
 * Head out to the Great Khan supply cave, located northwest of Bitter Springs, to find Oscar Velasco.
 * Talk to Oscar, asking him if he is the assassin will get him to divulge his opinion of the "refugee camp".
 * Bad Karma option: Convince Oscar to exact revenge upon the NCR for killing his family (Speech check of 50 required).
 * Good Karma option: Convince Oscar to let go of his anger and move on, returning to the Great Khans (Speech 50).
 * Head back to Bitter Springs and talk to Gilles again, tell her you have solved her problem to complete the quest.

Detailed walkthrough
Head down to Bitter Springs which is located east of the Brotherhood of Steel Safehouse. If you follow the road east of the New Vegas Medical Clinic all the way, Bitter Springs should be just to the north near the end of the road, when the road curves north. Talk to Captain Gilles who should be located in a tent behind the infirmary at the back the town. Ask her about Bitter Springs and she will mention that someone is picking off her people at night. Pursue the issue, and she mentions that 8 refugees and 3 NCR troopers have been killed, always by a single bullet to the head. She knows the assassin is hiding up in the caves somewhere but she doesn't have the manpower to go searching for him.

After conversation, the quest marker points to an area slightly northwest of Bitter Springs, almost directly east from Bloodborne Cave. The easiest way to reach this place is to head up behind the NCR tents until you reach the second Great Khan Supply Cave. Facing the entrance, hug the wall left of the cave and head back towards Bitter Springs. You should be unsuccessfully climbing a steep hill. Soon enough you will be able to fall onto a large rock attached to this hill. Get on the rock then continue trying to climb the hill while moving forwards and falling down onto some more rocks. You'll reach flat ground after the rock and can head towards the marker. You'll find a valley full of some small rocks. Hug the right wall of this valley until you can see a very slim opening in 2 large grey rocks. Also, when you get to a rock that has a small tree growing on it, look directly to the north and you should be able to see the opening leading up to the cave.

Once inside the cave, a Great Khan known as Oscar Velasco will talk to you after setting a few steps into the cave. If you're disguised as NCR or have Boone as a companion, he will shoot on sight. Picking the first conversation option will immediately turn him hostile. Asking him if he is the assassin will get him to divulge his opinion of the "refugee camp". You learn that he is trying to exact revenge upon the NCR for killing his family during the Bitter Springs massacre. Passing a speech check of 50 will allow you to persuade him to either leave peacefully or exact revenge upon the people responsible, the NCR. He will run off to Camp McCarran and undoubtedly get killed, resulting in bad karma. The best option is to persuade him to head back to Red Rock Canyon. He will give you a key which unlocks the gates in the Great Khan Supply Cache's located around the mountains, also resulting in good karma. The cave has two ammunition boxes with a small amount of .308 Caliber Rounds. The is also a gate at the entrance of the cave which the key unlocks, leading to a Great Khan Supply Cache (the item, not an extra cave), some scrap metal, a hunting rifle, another ammunition box and a footlocker containing a small amount of drugs.

Head back to Bitter Springs and talk to Gilles again and tell her you have solved her problem. This completes the quest.

Bugs

 * Even if you've been to the cave on top of the mountain and completed the quest, you'll get the reward, but the quest will still be active in your Pip-Boy as if you haven't completed it. Completing the quest No, Not Much should open up the Captain Giles dialogue tree about Oscar, even if you previously spoke to her and the option to tell her about Oscar was not available.

Behind the scenes
The quest name is most likely a reference to the 'Sound Of Music' song Climb Ev'ry Mountain (1965).