Small, white, self-illuminated disk over SE Bellingham foothills

After coming out of a LAN party with my college friends, a close friend and I walked out into the parking lot to chat about what we were doing next in the evening.
As my friend was talking to me, I continued to watch the skyline over the foothills of Bellingham (there is a beautiful view of mountains and the water to our west), noticing a "small white object" suspended over the top of the hill. As I noticed it start to move, I interrupted my friend and said, "hey, do you see..." and pointed. At that point, he said, "holy shit!" as we both witnessed this object, now clearly a white disk, ascend quickly in a semi-circular motion and quickly dart back down behind the foothill as if it had acknowledged it had been seen.
The craft would have been positioned positioned over the foothills of southern Bellingham, near the Fairhaven district or perhaps further south (difficult to gauge size/distance given the perspective). The object was white, in the classic disk shape, and was not reflecting the afternoon sun or giving off any lights of any kind - strictly self-illuminated. The entire encounter happened in less than a minute, but left a resounding impact on both me and my friend.