Corporal Sterling is a soldier dedicated to the NCR. He was, at one point, a Ranger, and involved in the Hoover Dam Scouting campaign of '73 (prior to the first battle to take place in '77), but has since fallen on hard times. While patrolling the Mojave Wastes near Malpais, he was captured by Legion slavers.
Under their brutal incarceration, he was viciously tortured and maimed, with his captors severely mutilating both his hands and feet. After they were done torturing him they left without tying him, figuring he wouldn't be able to escape. He then crawled out on his elbows and knees to the edge of the camp and rolled down the hill into the Colorado river, where he was then rescued by some observing rangers.
Unable to continue working due to his grievous injuries, he was discharged. Lieutenant Gorobets requested that Sterling be transferred to 1st Recon, believing that while he may not be able to do the trekking required for a Ranger any longer, he can still be an asset to the NCR as a sharpshooter.
He mentions he was captured near Malpais. This might be El Malpais National Park in New Mexico. But this is rather out of the way, and surely the NCR would have found Hoover Dam by then if he made it out that far, rather than a year later.
If the entire 1st Recon group isn't in a group at Camp Forlorn Hope they could all be split up and in different buildings around the Camp.
There is a cell found within the GECK, above the eastern cliffs of the Colorado River and across the river from Camp Forlorn Hope, named "MalpaisLegionCamp", perhaps alluding to Sterling's capture by the Legion near Malpais.