A stealth type rectangular shaped object flew east bound along Portola at approximately 100 mph. It was non-reflective black, no lights, no noticeable windows, no markings, no landing gear, no propellers, no vertical stabilizers, no jet engine pods, silent, definitely not amateur hobbyists drones or model airplanes. It was approximately 200 to 300 in elevation over these foothills adjacent mountain ranges. It was 30 to 40 feet wide, 10 feet long, flat with a thickness approximately 5 feet, flew like a flying wing without swept back wings like on the stealth bomber. There was no aircraft above it towing it by cable. I’ve been an amateur astronomer for 10 years, skywatcher for 4 years, I’ve piloted a single engine propeller piper cub before. I’ve watched most UFO documentaries for the past 40 years, and I’ve never heard of a sighting with this description. When I first saw it I thought of our stealth fighter and bomber. However, this was nothing like them. I didn’t feel that it was a UFO at first. I felt it was military. But we don’t have anything like this. This was way more advanced than a stealth fighter or bomber. I now doubt even Area 51 doesn’t have one of these in R&D. Feel free to contact me if you have questions. I didn’t even bother to try to take a picture with my phone as I would have missed those precious few seconds. This is opposite of all this intentional to be seen lighted UFOs like from project blue beam. This was sinister in appearance, and I doubt anyone else saw it. I’ve reported a hologram type UFO to MUFON over 20 years ago. This was no hologram; this was a physical object. I’ve read reports of some amateur drone hobbyistbguy here in South Orange County intentionally trying to get people to report a UFO just for the fun of it. The police know him and asked him to stop. This is not even a military drone. I’m not aware of this kind of technology.