Passing by Magic Mountain in Los Angeles, I thought it must be a themepark ride in the sky

My husband and two children were driving on the freeway to Southern California to go to Disneyland the following day and it was about 10:00 pm as we were passing the Six Flaggs Magic Mountain theme park.  For some reason I looked out the window on the driver's side and saw a large rounded disk hovering in the sky at an altitude of about 500 feet.  It must have had a diameter of at least 50 feet. It had flashing, sychronized "chasing" colored lights going around its diameter.  I couldn't tell the color of the "craft" as it was dark, but it appeared a dark silver. It just quietly hovered still in the sky and I thought at first it must be some novel attraction of the theme park, but I didn't understand how it could just hover with no propellers or wings.  A couple of times it moved very quickly sideways.  My husband didn't see it and the kids were asleep in the back.  It happened almost 30 years ago, but I will never forget it.  I expected to hear something on the news about it, but never did.  I wondered if I was the only one who saw it.  I am sorry I had no camera with me because no one believes it.
Date may be approximate, although the witness does not indicate that fact.  PD