This goes back a long way to December 1975. For obvious reasons I never reported it.

Traveling cross country from Houston TX, to San Diego, CA, I slept in El Paso Texas, then headed west on Route 10.   About 25 or 30 miles into Arizona, I stopped to stretch my legs in the desert.  The weather was exceptionally clear, stars were almost on the horizon and there was a full moon.  One maybe two cars passed in the roughly 15 minutes I was there.
 Looking South to Southeast, I saw an array of lights just over my right shoulder, close to Zenith, slightly to the West. I listened for a sound but there was none. I first thought it might be a helicopter. Its overall shape was indeterminate except for the elliptical/oval array of lights which were sharp and distinct. There were two (2) colors of lights, evenly spaced, alternating blush red, and a sort of mercury blue. For a minute or so it was motionless, perfectly stable as I tried to make out an overall shape, determine what it was and it’s altitude. Not knowing its altitude or size I couldn’t estimate either. I guessed that the elliptical shape of lights could be circular depending on its aspect or tilt.
 It then moved purposefully but slightly to the North, then back just a little toward the South, and stopped. From a full stop it then instantly accelerated over the Eastern horizon in what I estimated to be about 4-5 Seconds. Its path was perfectly straight without any random motion or bobbling. I stood and waited for about a minute believing I’d hear a sonic boom but there was no sound, sonic boom or otherwise. A diffuse blue contrail was left in its flight path, perfectly illuminated by the moon. This gradually turned to very thin white puffs and disappeared. No other aircraft were in the area.
 I thought about what I’d seen.  Thinking the Eastern mountain ranges were maybe 5K to 8K feet in altitude, it seemed to clear them by about 5K feet (estimate) so I assumed the craft was maybe at 12K-15K feet altitude. My confusion was how a craft or a missile could go from a full stop to 3 or 4 miles per second without any sound.
 I’m not exactly an untrained observer.  For 10 years I worked on the development and launch of more than 20 rocket-borne and reconnaissance aircraft systems.  After that I worked on Apollo instrumentation systems and was at the Flight Control Operations Directorate at the Johnson Space Center in Houston during Apollo 15, 16 & 17, and Skylab I, II, and III.
 For what it’s worth to you, there you have it. It’s been a long time, but I can visualize it as if it happened today.