Silver saucer shaped craft seen clearly over Sierra Nevada mountains for a short time.I am fomer USAF Metals Processing Specialist. I have worked on many types of Aircraft, military and civilian. So I know my aircraft by sight and sound. I have never seen anything like this before and I got a very good look at it.It was a shiny silver, like polished aluminum, completely round along the horizontal plane and yet about 1/3 that size in the vertical. To me it seemed about 50 feet in diameter. What really shocked me was it's flight characteristics. I flew manuevers I have never seen any plane accomplish and it was completely silent. It I was not looking directly at it... I would have never noticed it.It came over the mountain tops over the edge of the ridge, so it could be seen clearly from the valley where I was standing. It then abruptly turned a 180 and headed directly back over the ridge. But what was really amazing was during the 180 turn it also completely flipped over on it axis! So it was basically heading back over the ridge on its bottom...or upside down. If there is a top and bottom.Anyway, this short sighting was very profound to me. Since I know planes and this was nothing I have ever seen and the propellants produced no noise....whatever it used. That too was shocking.So there it is...I know what I saw and it was very clear, though very brief.What really shocked me later, because I live in a small community we tend to know all our neighbors. Where I live they are mainly cattle ranchers. They run them on open range up there on the mountain tops. We had two cattle mutilations reported up there over the years... I really was blown away when I learned this...because it seems just like other reports. I found that to be very strange.Let me impress upon you.... I am a very honest person... I strive to be all my life...this was no hoax.You can easily verify my story about the mutilations...the local law went up there and documented the cases. It was later in our local papers.((NUFORC Note: Witness indicates that the date of the incident is approximate. PD))