DEATH VALLEY, Calif. -- Rangers are taking stronger measures to try to prevent visitors from driving on dry lake beds and other fragile areas at Death Valley National Park.

The National Park Service said Tuesday there have been additional incidents since last summer when someone drove on famed Racetrack playa, leaving tire tracks that may remain visible for years. Damage has also occurred at Badwater.

Large new regulatory signs will be installed, more posts will be placed along the Racetrack shoreline and volunteers are being recruited to spend time there.

Racetrack playa is the site of tracks left by mysterious moving rocks which researchers believe are activated by rare interactions of rain, ice, wind and slick mud.

This month, volunteers from Longwood University in Farmville, Virginia, raked out vehicle tracks left at Badwater playa.