Silver oval shape-changing object seen west of Sahuarita, Arizona in broad daylight

I was driving my children to school when we witnessed an oval-shaped, bright, silver-white object in the sky. We had stopped at a traffic light and watched the object moving north. It was west by southwest from our location and appeared to be moving over the mine tailings that are west of I-19. The object moved north a short distance, then changed shape. As it changed shape, it “sandwiched” into a flat line then vanished. My son and daughter witnessed this with me. My son said “that has to be a UFO!”. At the time of the sighting, it was daylight, with clear skies.