There are many natural occurrences that might puzzle a traveler. One of them is Al Naslaa Rock Formation, located in Tayma oasis, Saudi Arabia. Recent archaeological discoveries show that Tayma has been inhabited since the ancient times.
Al Naslaa is one of the most photogenic petroglyphs in the area. The perfect slit between the two standing stones and the flat faces are completely natural. Note the small pedestals supporting the boulders. How long will they remain balanced here? How did the cut in the middle happen?
Most likely the ground shifted slightly underneath one of the two supports and the rock split. Could be from a volcanic dike of some weaker mineral that solidified there before everything was exhumed. Or, it could be an old pressure crack (you see a parallel crack just to the right of it) that has been pushed/pulled apart some. Or, it could be an old (minor) fault line, since fault motion often creates a zone of weakened rock that erodes relatively easier than the surrounding rock.
Location: Tayma, Saudi Arabia
– via saudi-archaeology.com
ALK3R 
Interesting. One can almost imagine they are two faces looking outward.
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For this to be a natural phenomenon would be fortunate and highly unlikely. Without having the co-ordinates or the benefit of a satellite aerial shot, it is reasonable to assume from the two photos available that this rock has been chosen and cut in this manner to determine seasonal changes based on the position of the rising or setting Sun.
The low altitude of the Sun in the photo of the rough face of the megaliths suggests it cast a bead of light as it was rising. This would of course be different at different times of the year as the Sun rises earlier or later, and observation over a period of just two years would allow the megalith to be calibrated based on the length of the resulting shadow when it is bisected by the ray of light, ensuring a higher level of accuracy than could be achieved from a shadow alone.
Though the cut between the rocks is impressive, equally so is the front face, which would appear to serve no purpose unless it was (as I suspect) aligned North-South to mark midday. “Was” – this would not be the same as midday today because the orientation of the Earth shifts due to precession, which is actually good news because from the difference we can calculate when the megaliths were erected. If anyone has more information on the orientation it would be of interest.