Lights only, no sound, moving across the night sky, then making a series of perfect right angle turns, like plowing a field.

One evening in the Spring of 1960, a friend and I were sitting at a softball field.  We were both 11 yrs old. 
 We looked up in the sky and both observed a pulsing light that was moving south across the desert sky. It was totally silent.  It would cross from left to right, then make a perfect right angle turn, go a short distance away from us and make another 90 degree turn to go across the sky to the left. Then it would make another right angled turn away from us, go a short distance and turn again to the right and go across the sky. 
This pattern, as if the light was plowing the sky, the way a tractor would plow a field, continued for several minutes until it disappeared in the distance. The next morning I went back to that ball field just to look around and found some pieces of official looking paper, like government letterhead, on the infield dirt.  I could see where it said US Air Force at the top in a blue ink. There were burn marks on the paper. That's all.
Witness indicates that the date of the event is approximate.  PD