Death Valley

During the virtual field trip to Death Valley, one of the most intriguing stops was the stop at racetrack playa. The surface of this area is almost completely flat with polygonal mud cracks covering the area. The area is really intriguing to me because there are several rocks that have been sliding around the surface of the area and no one has an explanation yet. The question that I had after visiting the area is, what is the force that is making the rocks slide? To find the force, I would first try to rule out the obvious by observing the rocks composition and see if they have magnetite, or to check if the area has a slope that might cause the rocks to slide down. I would also check for any type of erosion going on that might be moving the rocks like wind or water. I'm sure these things have been checked on already but those would be my first options.