I respect the skepticism. I do not subscribe to the 'UFOs are aliens' idea myself. Though in this case I believe the OP did see what he claims. There's a longstanding rumor that some branch of the armed forces is in possession of a 'stealth blimp'. Exactly what a 'stealth blimp' is, I don't know. But there have been numerous sightings over the previous 20 years that match very closely with that OP saw.

I think most "credible" UFO sightings (especially those in the western US) are Government owned aircraft. For the most part, Humans are just bad at interpreting what they have seen. One of my favorite examples is the rumored "flying artichoke" that was likely just a sighting of an F-117A Stealth Fighter ( http://i.imgur.com/D22OrQ1.jpg )