GPS lock in mountains

HI gang.  I had a weird thing happen to me the other day.  My family went camping in Woodland Park, CO [Elevation: 2543 metres (8344 feet) ].  It's just up the road from Colorado Springs, where I live.  I was tracking our progress with Navicomputer.  When we hit the canyon, I lost GPS lock.  I figured that wasn't a big deal, since we were going 50 mph, up a narrow winding mountain road.  However, the disappointing thing is that when we eventually made it to our campsite, I still could not get GPS fix/lock.  We were out of the valley, and had plenty of clear blue sky, but according to Navicomputer, it couldn't ever find more than 3 satellites, and never would lock on.  Actually, it did lock on with 3 once, but it thought I was in New Mexico!  I started to worry that I had broken my GPS when I dropped the phone a week earlier, but it's working fine back in town.
  Has anybody else seen a similar problem?  I don't know what to attribute it to.  (maybe it's NORAD interference in Cheyenn Mtn...  )

Thanks Bruce.  The camp site is right on the edge of cell-phone range, but since I don't have a data plan, I always have AGPS disabled.

I recently travelled out of state, and GPS stopped working. It started working again when I updated AGPS, even though it wasnt due for an auto update until a few days.
Even if you have that disabled, it might be your problem.