GLAMIS, Calif. - Every Thanksgiving weekend, tens of thousands of people descend on a remote corner of the Southern California desert to test their off-road driving skills in the wind-sculpted sand mountains of the state's largest dune formation.
''It's awesome,'' said William Pedraza, a 20-year-old mechanic from Whittier riding a 3-wheel all-terrain vehicle. ''There's nowhere you can get this many people and conditions this perfect.''
But the off-road enthusiasts faced new limits this weekend.
The U.S. Bureau of Land Management, in response to a lawsuit brought by environmental groups, closed 42 percent of the Imperial Sand Dunes Recreation Area to motorcycles, dune buggies and other off-road vehicle use.
The agency also brought in additional rangers and sheriff's deputies from Imperial County to crack down on unruly behavior that has resulted in scores of arrests and citations in recent years.
It's made for a tense weekend in some parts of the 40-mile-long recreation area near the Arizona border as law enforcement authorities set up checkpoints, environmental activists monitored closed areas with video cameras, and off-roaders bristled about the closures.
Authorities arrested more than 30 people as of Saturday and issued many more citations, mostly for drunk driving or other alcohol-related offenses, said Clark Beene, a supervising ranger who estimated the crowd at slightly more than 80,000.
Meanwhile, volunteers with the Center for Biological Diversity of Tucson, Ariz., and other environmental groups logged more than 100 encroachments into closed areas while their opponents among the off-road advocacy groups vowed to reverse the closures.
Similar controversies over the use of public land occur regularly throughout the west, most recently with the decision by the Park Service to phase out snowmobiles in Yellowstone National Park and a proposal to eliminate parking spaces to reduce traffic in Yosemite National Park.
In the Imperial Sand Dunes, which start about three miles north of the U.S.-Mexico border, the environmental groups insist that off-road vehicles are destroying a fragile ecosystem.
Off-road vehicle advocates deny the charge.
''There seems to be a concerted effort to lock this country up with respect to outdoor activities,'' said Mark Harms, owner of an off-road tire store in Temecula and an active member of the American Sand Association. ''There's going to be nothing left to do if this keeps going.''
The Imperial dunes area is a harsh environment where summer and late spring temperatures regularly exceed 105 degrees and General George Patton trained his troops for desert warfare. The area buzzes with off-road vehicles during the winter and fall, but Thanksgiving is the busiest time.
The Center for Biological Diversity, Sierra Club and Public Employees for Environmental Responsibility sued the Bureau of Land Management, claiming it wasn't protecting a threatened plant called the Peirson's milk-vetch.
To settle the suit earlier this month, the BLM agreed to close about 49,000 acres in five spots to protect the plant, a woody perennial that sprouts purple flowers in spring and is known only to grow in the Imperial dunes. The closure left some 68,000 acres remaining for the off-road vehicles.
''This is a unique plant and before we lose it forever we think it's a good idea to give it a chance to survive and maybe make a comeback,'' said Daniel Patterson, a desert ecologist with the center.
The closure is temporary until the federal authorities develop a management plan for the dunes. But Harms and others in the American Sand Association suspect the environmental groups hope to force the government to make the closure permanent and expand it to cover the whole area.
Association members say that off-road enthusiasts have been unfairly and inaccurately cast as rowdy enemies of the environment. Harms and others describe the typical visitors to the dunes as families who spend thousands of dollars on equipment and are more likely to avoid plants to prevent damage to expensive tires.
The BLM began marking the closed areas this week with bright orange fiberglass stakes spaced about 60 feet apart and marked with small signs that say ''no motor vehicles.'' In at least two of the areas, many tire tracks were visible in the soft sand.
The agency hasn't issued tickets for entering the areas because all the signs aren't up and motorists are learning about the closures, said BLM spokeswoman Roxie Trist.
As Patterson watched a motorcyclist and an all-terrain vehicle appear to blatantly encroach into a closed area - repeatedly racing through the stakes - he also threatened legal action. ''If this is what's going to happen, then this is obviously not going to work,'' he said.
