Death Valley's moving rocks

Several years ago, Noel Jenkins wrote a resource as part of the Action Plan for Geography, for the Royal Geographical Society's website.
It described the sliding stones of Racetrack Playa
It's a favourite of many teachers...

Recently, this story has come back to prominence as a report has claimed to have worked out what the mechanism is that lies behind the moving stones.
Time to bring this little mystery back out perhaps...

Image copyright: Noel Jenkins