I would very much doubt that sand erosion would cause those patterns only on those rocks and no where else in the area. I have seen some interesting hypotheses suggesting that the sphinx enclosure was flooded regularly so that the "Sphinx Island" would have stuck up out of a sea. This would easily have been accomplished via the Nile. The "temple" that was found leading up to the Sphinx is oddly enough arranged that it could have formed a fourth wall, enclosing the Sphinx enclosure and potentially becoming capable of holding in water.

Regardless, I flat out reject Hawass' notion that it was built by Chefren as wholly inadequate at explaining obvious signs of age.