3 white lights in a triangle in a stationary small cloud in a cloudless sky turning every 2-3 seconds 2 hours then off

I was an an army officer, an O-3 Captain, observer controller Stationed at Fort Irwin, part of the Cobra or Armored Task Force Team - we were essentially range police, coaches and controllers of Battle exercises with Units who came in from all over the United States. It was near midnight and I was traveling from North to South in my HUMMV, alone. There was an assembly of a logistics group ( maybe 30 vehicles) at 1500-200 feet I listed above. It was a cloudless dark night, but at the coordinates, there was a small cloud 1500-2000 feet above the assembly. As I got closes I saw there were 3 white lights in a triangle shining down from inside the cloud. Every 2-3 seconds at a regular interval, the light would rotate a third of a turn. The people in the Assembly area assumed it was something to do with the range and didn't question it. I called another 0-3 Captain on my radio net who I knew was in the area, and he saw it too, described it the same way, and also had no idea what it was. I called range control, who verified there were not aircraft in the air anywhere on the base that night…I asked to check again, and he called the airbase that was supporting the exercises, and they said they had no aircraft here. It stayed there at least two hours. At some point the lights stopped, and the only reason I knew the cloud was still there was I could not see the stars through it. I looked away a second and then the cloud was just gone.