While driving north toward Idaho through northern Utah, I cross over a low pass when I noticed a very large object hovering just above a ridge approximately 1/2 mile to the NW of me. Continuing to drive north the tan colored long cylinder shaped craft rotated with its lower side toward me, at which time I could see that it actually shaped like a triangle with a concaved side and two straight sides. The craft appeared to be three to five hundred feet along each side of the triangle, forty feet thick from top to bottom, a dull tan color with a darker brown circle on the bottom. As the craft rotated to about a 60 degree angle it moved slowly down behind the ridge. I heard no sound from this object. I watch the craft for 2 to 3 minutes while driving north. Knowing that over the next ridge I could see to the SW for miles, I sped over the ridge to see the craft again but the canyon was empty. I do not know what this object was, but I do know that I saw something unexplainable.