Sliding Rocks of Death Valley

Alright so I was reading about these huge rocks (some 700 lbs) in Death Valley that would move on their own. No one has seen them move but they somehow migrate from one spot to the other.  Your mission is to try and figure out why.  Start by thinking up some of your own theories, then move on to doing some research. Please list your ideas here first then look up the answers.  Below I have included an exert from an article that may explain more.  Good Luck!!

"One of the strangest occurrences that Dr. Bob has ever come across is the mysterious sliding boulders of Death Valley National Park, California. There are trails showing that boulders up to 705 pounds (320 kg) have moved large distances over flat terrain. No one has actually seen these boulders move.

Death Valley National Park is a protected desert region with an area of 2,067,628 acres. It receives less than 2 inches (5 cm) of rain a year. Some of the world's highest air temperatures (134°F/57°C) and ground temperatures (165°F/74°C) have been measured there. Within the park is an area called the Racetrack Playa. A playa is a nearly level area at the bottom of an undrained desert basin that is sometimes temporarily covered with water. The Racetrack Playa is where the mysterious sliding boulders are found.

What is causing these boulders to move? Gravity sliding is clearly out of the question. The Racetrack Playa is incredibly flat, so much so, that on a calm day only 2 inches ( 5 cm) of water will entirely cover the playa. " -Doctor Bob's Science Site http://www.frontiernet.net/~docbob/science.htm