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
There are several Great Khans supply caves around Bitter Springs, two of them immediately north of the camp. The first contains several Giant Ants, while inside the second are some Young Night Stalkers. Each cave also contains a locked gate, behind which are what remains of the Great Khans supplies.

The third cave is located further north-west of the camp, at the end of a small pathway. 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 (presumably one can also loot the key from his corpse should a less diplomatic approach be taken).