Enormous white triangle craft with point straight down.

A friend and I were walking a dog on east bound US Forest Service road #336 heading toward Apache Lake AZ from the Mills Ridge Forest Service Road #429. We looked up and saw an enormous white triangle craft oriented with the one point situated straight down. The craft appeared to be a bit longer than wide. In three seconds the craft narrowed and then disappeared - it did not fly off. One instant it was there and the next instant in time it was not there.
The craft was enormous as we could compare it to the mountains on the east side of the Salt River Canyon. It was about 1/3 the height of the mountain side which mountain is estimated to rise 2000 feet from Apache lake level. I estimate craft was between 500 and 1000 ft in length.
The craft was approximately 2.5 miles from us as measured on Forest Service map. From this close distance it was simply enormous.
There was no noise, sound or exhaust from craft.Color was a milky white with sharp distinct edges. No lights were observed and craft was not reflective. Weather was clear and the temperature was in the 60s Fahrenheit.
Sighting spot: (33.6731349, -111.2189123)
Craft spot: (33.6572906, -111.1776200)