The shape and too big to be flying that slow

Some back ground.  I have been in aviation since 1969 (military and civilian) and I was employed at NASA Dryden Flight Research Center, Edwards AFB as a aircraft inspector. Going to work for a shuttle landing.  At approx. 2:30 AM on highway 395 between Adelanto and Bleekers Corner (intersection of 395 and 58)  This was a clear night with lots of stars. There was mountain and desert back ground.  
Driving north about 11 miles from Adelanto, my vehicle stopped running.  I got out and to my left I saw a object in the sky.  It was very large approx. 300 ft. wide and approx. 600 ft. long moving slow. It was a delta shape, but the front was flat, approx. 50 to 75 ft.  It was dark in color (could not really tell in the dark) with no projections, no sound, no lights.  I noticed it due to it blocking out the stars.  It was moving north. I watched it until it was out of sight.  I thought  "it was moving too slow to be that big".  I know it was not a blimp.  My vehicle start! ed and I proceeded to work.  At work I asked if anyone saw anything to the south, no one had.
In my career I have seen a lot of strange aircraft, but nothing like this.
Witness indicates that the date of the incident is approximate.  PD