Disc-shaped UFO over Corte Madera, California

On September 1st, 2015, an automobilist drove towards Corte Madera (in California) when he has spotted an impressive and glowing disc-shaped UFO in sky. He took five photos of this unidentified object.

Witness statement:

Pictures of ORB attached. Not sure how to start other than to tell what I saw today. I was driving over the Richmond San Rafael Bridge from work towards Corte Madera, CA today 9/1/15 at 3pm and I saw this extremely bright almost chrome-like sphere hovering over San Quentin prison. It had a little bit of a blue hue to it and looked like it was rotating or pulsing. I couldn't pull over on the bridge and lost sight of it behind the hill. I was sure I'd catch it in the pass between the Bridge and Larkspur Landing, so much so I got out of my car at the shooting range there and was perplexed that it wasn't there. I got back in my car hoping to see it again near Corte Madera. I was looking all over and when I was passing the Ferry Parking lot I saw it over the marsh by the Village shopping center South of the 101. I lost site of it at the hill next to the parking lot because it was heading towards Mt. Tam. It was very low in the sky. I debated whether it would be easier to see it again from the back of the Ferry or to go to the 101 South. I chose the hwy and was shocked I couldn't see it from the on ramp because it gives a very open view of the terrain. I was looking frantically to my left and only glanced to my right to turn off the freeway and spotted it on the opposite side on my far right between me and the north hill of Corte Madera. I pulled over immediately and used my work iPad to quickly snap 5 pictures in rapid succession. I decided I would stay put and not take my eyes off it because I had a goid vantage point (as you can see in the pictures). After 15-30 seconds it appeared to almost fad into itself and disappear. This transition took about 5 seconds. I sat there baffled and was looking at the hill behind the object to ensure I wasn't just seeing a massive reflection but there were clearly cars that had nearly no reflection on that route of the hill. The pictures don't show how bright this thing truly was. It was like looking into the sun. I retraced my drive and the object was seen unequivocally in different locations from multiple vantage points as they are separate lines of site. Please let me know what you think this is!!!