UFO Sighting in Flagstaff, Arizona on 2017-07-01 16:30:00 - Large, disc-like object, moving slowly east to west, gradually "pixelated" and disapeared

On the afternoon of friday, july 1st, 2017 at about 4:30pm. i was doing yard work in my backyard. i sat down in my lawnchair to take a short break and leaned my head against the back of my chair and looked up. almost straight above me, but more to the east of my home, i saw a disc-like object moving very slowly towards the west at a very high altitude (approx. 30k ft.?). it appeared at first to be stationary but as i staired at it i could tell it was moving in relation to the tree i was sitting near, in my backyard. i thought through all of the things it could be (plane, balloon, drone, etc...), but judging by behavior, shape, altitude and size, i came to the realization that it was a ufo. it appeared to be flying at or above about 30k ft (in clear skies) and the size of about two passenger jets side by side, it was tan in color and shaped like a doughnut with edges that tapered to a point and in the center instead of a hole was a sort of dome at the bottom (i never saw the top of it). i went inside my house to get my phone to take a picture of it. i took two photos, but after viewing them on the phones screen i felt that they were not good enough and unfortunatley i deleted them. i'm still mad at myself for doing that. as i continued to stare at it clouds were beginning to form to the west of it and they cast a shadow up on to the craft. minutes before passing over the clouds it started to rotate (or bank to the north) then the most bizare thing happened and the best way i can describe it is it sort of "pixilated" like a wave moving over it from one side to the other it took about three or four seconds to just vanish. it didnt fly away, it just disapeared. the entire event lasted approx. fifteen minutes from the time i first noticed it. i've seen strange things in my life but nothing as definitive as this. i needed to tell someone about this.