I got to see two of them in flight together. We were just summiting the Sierra Crest just south of Mt Whitney and a bit North of Edwards AFB we could see over 100 miles in any direction. We happened to be looking west just as these two black specs appeared just a few hundred feet above the terrain. They came right at us and directly above us they inverted and dove down towards the desert floor. The sound/shock wave was intense. The flipped back over and still hugging the terrain shot over to the Ruby mountains leaving twin dust trails across the desert then they went up and over the Ruby Mountains and out of sight in less than 30 seconds, We were awestruck. This was in 1976 or 77