Tire tracks run along "the drag" adjacent to border marker 210, a monument marking the border between the United States and Mexico, in the vast expanse of the Imperial Sand Dunes.

12:07 a.m. April 21, 2005

IMPERIAL SAND DUNES The man at the wheel of a roaring dune buggy rips a swirling trail over the desolate landscape on a morning ride. He veers to the south, and then whips back.
That prompts U.S. Border Patrol agent Danielle Suarez to pull him over and give him a warning. The dune rider doesn't know it, but he just crossed into Mexico and back.
Here, along a five-mile stretch of constantly shifting sands, the border is invisible. It's an opportunity for drug smugglers to slip over the line and mix with the off-roading crowd and a challenge for the agents trying to spot them.
At one point, the international line sits just a half-mile south of Interstate 8, the main link between San Diego and Phoenix.
The Imperial Sand Dunes, a desolate desert expanse, is a giant playground for all-terrain vehicle enthusiasts. On busy weekends between fall and spring, when the temperatures are tolerable, ATV riders, dune buggy fans and campers in motor homes swarm over the sands. A holiday weekend can draw close to 200,000 people. "It's so easy for them (smugglers) to blend in, looking for a way to get onto I-8," Suarez says as she meanders the hills in a pickup truck. "There's really nothing separating the two countries."
The southern edge of the dunes, the Buttercup Dunes, is remote enough to have served as a film location for parts of "Star Wars: Return of the Jedi."
The only marking for the international border: a couple of concrete obelisks about 15 feet high.
Since late February, there have been seven drug busts along the dunes, and a string of others before that. Federal agents have yet to uncover any elaborate criminal enterprise, but the arrests show how the dunes are being used to funnel dope into the United States. Marijuana smugglers appear to have used Buttercup since about 1999, said Ricardo Sandoval, special agent in charge of the Homeland Security Department's Immigration and Customs Enforcement bureau in El Centro, about 35 miles west of the dunes. He declined to elaborate.
In one typical bust last month, a Border Patrol agent spotted seven all-terrain vehicles streaking across the border at sunset five of them with large duffel bags strapped to the seats. At the main campground, two men loaded the bags on a trailer.
Agents stopped the trailer on I-8 and found 558 pounds of marijuana in a secret compartment, according to charges filed in federal court. The driver said a woman in nearby Mexicali, Mexico, promised him $500 for each duffel bag. He admitted delivering four bags to a truck stop in El Centro a few days earlier.
If they don't mix with large crowds in daylight, smugglers sneak in under the cover of darkness.
Last May, Border Patrol agents spotted two abandoned ATVs about 150 yards from the border, shortly before midnight. They followed tracks and saw several ATVs cruising through the dunes without lights, heading for a campground. At a campsite, they saw several people loading bags from the ATVs into a trailer.
Agents seized 1,644 pounds of marijuana in 90 bundles at the campground, according to charges filed in federal court. Several drug runners escaped on foot as Border Patrol planes circled above. One who got caught said he was paid $1,000 to deliver the drugs to El Centro.
The Border Patrol's El Centro sector, which extends along 76 miles of the Mexican border in eastern California, has 68 ATVs in its fleet, up from only five in 1997. Four camera towers along the five-mile stretch of dunes beam images to a Border Patrol station about 40 miles west in Calexico, where they are monitored around the clock.
Some agents cruise in dune buggies, while others survey the landscape from perches that are up to 300 feet high. They look for dune buggies that carry duffel bags or appear to be holding lots of weight.
Sometimes, smugglers will send about 10 or 15 ATVs across, only a couple carrying drugs, said agent M.E. Schultz.
ATV "scouts" often scour the terrain to see where Border Patrol agents are roaming, agents say. They use walkie-talkies to tell contacts in Mexico where the drug-laden vehicles should cross.
"When they feel they don't have a chance, they just turn around and go back," agent Gerardo Guerrero said during his morning patrol.