Climb Ev'ry Mountain

 is a quest in Fallout: New Vegas.

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, who has been hiding in one of the hillside caves to the north of Bitter Springs.

Quick walkthrough
The sniper is located in a cave north-west of Bitter Springs (north-east of Bloodborne Cave), at the end of a small path. This path can be very difficult to locate as it is well hidden among rocks that cannot be climbed and are very easy to become stuck in. Just before the path you might find several fire geckos inhabiting some red rock; the path is just to the north, when you enter back into grey rock, and is slightly to the right.

Inside is Oscar Velasco, a member of the Great Khans who lost his family three years before and now seeks vengeance by killing the occupants of Bitter Springs. He can be convinced to let go of his anger and move on to Red Rock Canyon with a Speech check of 50; if successful he will also give the Courier a key that unlocks the gates to the supply caches located inside each of the caves for the quest No, Not Much.

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. Persue the issue, and she mentions that 8 refugee's and 3 NCR troopers have been killed, always by asingle bullet to the head. She knows the assassin is hiding up in the caves somewhere but she dosen'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 side 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 movng 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. Picking the first conversation option will immediatly 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 do one of two things. The second option is to make him 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 Greak 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
In the cave Oscar is hiding in, there is a gate to the left of the entrance corridor, and another corridor to the right, opposite the gate. If you follow this corridor, there is a bear trap on the floor near the beginning, and three frag mines near the end. The mines are lined up across the corridor with the one on the right sitting still and unarmed, while the two on the left are glitching in and out of the corridor floor. These two frag mines are also unarmed, but much more difficult to pick up.

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 in your Pip-Boy as if you haven't completed it.

Confirmed above with xbox 360 as well. Quest still active, and marker still follows Captain Giles.