25' mirror ball traveling 60' up at 300 mph on a clear morning. passed about 100 feet from us .

Mirror like finish,very slight haze about 1' around it,  about 25' diameter.  It was traveling due West on 54 South Street and 80th West.  I was traveling due East. It was about 60 feet above ground, not twice as high as the power poles.  It was traveling about 300mph. I saw it for about 8 to 10 seconds, in which time it traveled about 2 miles.  It passed parallel to me traveling in the opposite direction, about 75 feet North of me, to my left.  I was East bound at about 50mph. At the closest point, we were about 100 feet away. It was traveling at a fixed altitude.  As it past me and crossed 84th West Street the ground raises up into the Ochure Mountains, it moved up and down as the ground rose and fell towards the foot hills.  I could see it coming for about a half mile, as it approached, I lost sight of it for about one second as it dropped below the horizon as the road in front of me (about 1/4 mile away) dropped off the hill side.  It came back up into sight as the road leveled out in front of me and then past us. I turned my head and watched it "contouring" with the land elevation change until it was too far away to see, about a mile or so.  Oddly, my wife (we were driving to work and were almost there, we worked at the Hercules rocket motor plant and Hercules Graphite fiber plant in Magna) didn't say a single word.  After about 5 seconds I asked her "did you just see something you'd have a hard time explaining to someone?"  She said "you mean the big mirrored glass ball that just flew past us?".   I said "good, then I'm not crazy!".  
There were no other cars on the road, no one around, it's now built up around there, in those days it was an industrial plant out in the dry farms.  It was just a few minutes before sunrise.  I've seen ball lightening ..and this was not ball lightening.  Clear sky, beautiful day.
Date may be approximate, although the source of the report does not indicate that fact.  PD