A layer of condensation under the rock frozen over in the early morning will aid its movement towards the Sun. As the sun passes low over the horizon sometime blocked by the surrounding mountain might explain the sudden change in direction as evidenced by the trail behind the rock. The Sun will be blocked over long period of time (weeks/months) for the Sun to change its rising position on the horizon noticeably.
All trails will have a slight curve as the Sun rises at a slightly different position each day and move slowly across the sky. Movement stops when friction under the rock increases as the condensation melts and dries up. Movement starts up again the next day on sunrise, towards a slightly different sunrise position, when the bottom of the rock is once again on a thin layer of frozen condensation.
And the psychological disorder to want to explain everything was once called religion.
