Death Valley’s mystery solved

The 'GPS stones' which were engineered to record movement and velocity, were stationed at the southern end of the playa where rocks begin their strange journeys after tumbling down a cliff.At the end of last year, Richard and James Norris returned to inspect the instruments."We found the playa covered with ice. We also noticed fresh rock trails near shards of thin ice stacked up along the shoreline," Richard recalled to the Times.