That “small” opening along the rock’s bottom in the first photo is man-made and larger than a garage door. In the 1930’s a religious group intended to hollow out the rock, but didn’t get very far.
It’s an alien ship! And the ETs are using memory-suppression rays so you’ll forget about it! If you don’t see this in the future, you won’t know!
July 31, 2010. Along US191, north of Monticello, Utah.