Rectangular craft hovering over mountain road

I was driving down on a mountain road when I saw a rectangular craft low in the sky directly in front of my car.  This is a remote area and I would have heard it if it was a plane but there was no sound. It was a dull gray but glinted in the sunshine. It was not moving like any aircraft I’ve ever seen; it just seemed to be hanging stationary in the sky.
 I slowed my car but rounded a bend where trees obstructed my view.  I knew there was a clearing around that bend and pulled over when I reached it because it would give me a clear sight line.  I got out of my car and turned around to see the craft without tree obstruction and it was gone.  It wasn’t more than a minute from my point of vision to arriving at the clearing – how could something that big just disappear from sight when it didn’t even appear to be moving?