Bill Fraley knelt to examine the brown, pebbled soil, like an art professor studying a familiar drawing.

“See those two fine-lines?” he said, passing a finger over two shoe prints, each with washboard rows of ridges. His hand moved to another heel print a few inches away. “And there’s a doper lug,” the heel imprint of a boot sometimes worn by drug smugglers.

A few steps away, a 5-foot barbed-wire fence cut through the cactus and greasewood, separating the United States from Mexico. The Border Patrol agent stood and tipped back the brim of his Stratton cowboy hat, eyes hidden behind aviator sunglasses. A satisfied expression hung on his chiseled face.

There were at least three of them, he figured. “It rained all day yesterday and these signs are on top of the rain,” he said. “So I’d say they crossed yesterday, between 6 and 7. And it looks like they’ve got heavy loads of dope on them.”

Their drop point would probably be on Interstate 10, near the exit for Steins Ghost Town and the New Mexico-Arizona state line. To get there, they would have to traverse 75 miles of rocky mountain ranges and tumbleweed-choked valleys, avoiding rattlesnakes and federal agents -- and do it on foot, with 45 pounds of marijuana on each of their backs.

It would take five to seven days.

Unless the Border Patrol caught them first.

Drug cartels in Mexico are in a deadly battle over smuggling routes into the United States. At the same time, more border agents, hundreds of miles of new fencing and a growing arsenal of high-tech devices have made it harder than ever for drug traffickers to cross much of the 2,000-mile border with Mexico. Over the last six months, the U.S. Border Patrol has seized 1.3 million pounds of marijuana -- an amount nearly equal to the total for all of last year.

The crackdown has driven waves of ever more daring smugglers to the most remote and rugged parts of the border, areas that are difficult for federal agents to patrol, where fancy electronic surveillance is often useless.

The southwestern corner of New Mexico, with its 81 miles of border, is one of those prime corridors, a forbidding area the size of Los Angeles County where drug traffickers find plenty of places to hide. To outwit their adversaries, Border Patrol agents here rely on tracking skills borrowed a century ago from Native Americans: “cutting for sign,” detecting where someone has crossed the Earth’s surface, and “pushing sign,” tracking that person down.

So far this year, Border Patrol agents in this area have hauled in 35,500 pounds of marijuana, more than all of the year before, with a street value of nearly $30 million.

Radar units, infrared scopes and other technological marvels “are damn good machines,” said Eddie Parra, a supervisor in the Lordsburg Border Patrol station. “But they can’t see everything here. It’s still up to us.”

Tuesday, 10 a.m.

Fraley cut the sign a mile from the nearest dirt road. He got on his radio to relay the details to other agents, who work as a team, in four overlapping shifts, 24 hours a day.

To Fraley, 50, sign-cutting is both art and science. He looks for footprints, though he usually finds just fragments. He looks for disturbances: turned-over rocks, broken twigs, bent barbed wire. He looks for chewed gum, a cigarette butt, the residue of a line of cocaine snorted on a rock. He looks for clues to fix the time: Prints that seem to run right into a tree, for example, were made before the moon rose.

It is, Fraley explained, “the ultimate hunt. They may not be able to read and write their name, but they are very, very good at what they do.”

On this morning, the smugglers had left behind plenty of evidence. They had knocked over rocks and Fraley and Parra noticed that the soil beneath was slightly dark and still moist.

“What I really love,” Fraley said, “is when you come across an ant pile that’s been stepped in. Ants will rebuild an anthill in an hour, so if you see a footprint in an anthill you’d better look up -- because you’re likely to be looking right at your adversaries.”

Drug smugglers are nocturnal creatures. They spend their days hunkered down in the latticework of rock caves in mountains on the Continental Divide, crossing the valleys and open countryside by night.

Fraley’s calculation: If the smugglers crossed the border at dusk, they had traveled much of the night. That likely put them near Red Hill, 15 miles north in the Animas Mountains.

A Mobile Surveillance System had been positioned on that route the night before. The tall, rotating radar device, operated day and night by an agent under camouflage netting, is the latest in crime-fighting technology. But it can’t see into the deep gullies that slice down the mountainside, and it hadn’t picked up any movement.

This group, Parra and Fraley agreed, would probably spend tonight moving through the Animas Mountains, which appeared in the distance, bathed in the blue shadows of puffy clouds. Tracking them through that terrain at night would be impossible. But eventually, the smugglers would have to drop down into the valley and cross westward to the Peloncillo Mountains.

That’s when the Border Patrol would have its best chance to catch them.

Wednesday, 1 p.m.

Parra’s radio crackled with good news. Seismic sensors in the Animas Mountains had recorded movement overnight, and that morning, agents on horseback had picked up the sign. It was the same group.

He steered his SUV along County Road 1, which runs through the long valley between the Animas and Peloncillo ranges. Thick whiskers of wild grass, toasted gold, stretched for miles on either side of the road. To the right, a twisting column of tumbleweeds rose 40 feet in the sky like a translucent tornado. To the left, a cloudburst showered a distant peak in indigo streaks.

Sign-cutting is Parra’s passion. “God blessed me with the skill,” he said.

A Border Patrol agent’s life can be lonely. Some patrol hundreds of miles a day in SUVs, a two-way radio their only companion. Others venture forth in pairs, on foot, on horseback or in all-terrain vehicles.

After dark, when the few ranchers around here park their pickups, the roads belong to the Border Patrol. “Any car you pass down here at night is either lost or pretending to be lost,” Parra said.

About 3 p.m., Parra, 43, pulled to a stop and met up with the horse patrol unit leader, Lawrence “Junior” Helbig. Helbig and his partner had spent much of the day tracking the footprints.

“It’s the same group,” Helbig said. “The odds of having several fine-lines and a doper lug together are just too high.”

Fraley had confirmed three sets of footprints; now Helbig had spotted two more. A late-morning shower had mucked up the trail, but the color of the soil in the prints suggested they were only about four hours old, he said.

It wasn’t so long ago that the Lordsburg force numbered barely a dozen agents; today it has 200, with plans for 350 in two years. The United States plans similar buildups all along the border amid fears that the violence in Mexico will spill over here. Helbig knows it’s still not enough to stop the waves of smugglers.

“It’s like stopping the flow of water in a river,” Helbig said. “You can throw a rock in it, but the water always goes around.”

Two weeks earlier, Helbig had tracked five smugglers into a nearby thicket. The smugglers jumped out and “quailed,” running in all directions. Agents caught them and found several hundred pounds of marijuana as well as an AK-47 rifle. One of the smugglers said the weapon was for protection -- from other drug smugglers.

“Thank goodness they’re not real violent toward us yet,” Helbig said. “But there’s a reason we carry a sidearm.”

Wednesday, 8:15 p.m.

Parra, tired after a 14-hour day, headed home to Lordsburg. Jose Portillo, 36, the night supervisor, set a trap.

He assigned two agents to hide on one side of County Road 1. Using thermal imaging binoculars, they would try to pick up the smugglers as they descended into the valley. Then they would radio another two-man unit, this one armed with M-4 rifles. If all went according to plan, the smugglers would never make it across County Road 1.

Portillo drove his SUV, headlights off, toward the stakeout. He wanted to be close when the trap was sprung. Jack rabbits bounced across the road. Taking care not to illuminate the brake lights, he coasted to a stop. The engine was idling, heater on. A gauge showed the outside temperature at 50 degrees, a 20-degree drop from a few hours before. The moon crested the eastern horizon, casting light on the 8,500-foot Animas Peak.

At 9:15 p.m., Portillo checked in with his two teams.

Nothing.

“Tonight is the night to catch them,” Portillo said, gazing out his windshield, Orion shimmering in the sky. “It’s harder after this.”

At 1:46 a.m., Portillo reached for the radio handset.

“Let’s pull out,” he told his surveillance units.

He didn’t try to hide his disappointment. “They’ve crossed by now,” he said. “They must have taken a different route.”

Pause.

“Tomorrow, it’s do or die.”

Thursday, 10 a.m.

Parra read the overnight report: The smugglers had crossed County Road 1 several miles from the stakeout, and made it to the Peloncillo Mountains.

Rogelio Villa and his partner, on foot in the Peloncillo range, picked up the sign. “We’ve got our guys over here,” Villa radioed Parra. “They were definitely here late last night or early this morning. Looks like there are four or five of them.”

The footprints were different, but Parra wasn’t worried. Smugglers often swap out their boots. “It’s likely these are the same guys,” he said.

Traffickers know that footprints can give them away. So they walk on rocks, where they don’t leave prints. They walk backward. They wear boots like those worn by Border Patrol agents. They tie strips of carpet to their soles to avoid leaving clear prints on dirt roads. (“I’ve even seen them take the hoofs from cattle and glue them to their shoes,” one agent said.)

Two agents jumped ahead to see how far the smugglers had gotten. At a cattle watering tank, they came upon a rancher’s motion-activated game camera. An agent took the memory card out of the camera and put it in his own.

The photo that popped up was clear: a muscular, dark-haired man with a short beard, wearing black jeans and a sweat shirt under his striped shirt. A water bottle in his hand had been shrouded in black cloth, to avoid a reflection that might give his position away. On his back was a parcel, about 3 feet square. Marijuana.

As Parra knew, nearly identical parcels from an earlier bust, each weighing more than 45 pounds, were stacked in a drug locker at Border Patrol headquarters.

Parra called in air support. Fifteen minutes later, a low hum signaled the arrival of a single-engine plane, which made long, sweeping runs over the mountain range.

“We don’t see anything,” the pilot radioed. “We’ve probably dug them in like a tick. You might walk right up on them.”

But Parra thought the smugglers might have moved farther north, across Highway 9 to the rocky hills of Weatherby Canyon. If the traffickers had reached Weatherby, they would be one night’s hike from drop points on Interstate 10.

Villa found fresh footprints in the canyon, confirming Parra’s suspicions. “These boys jumped Highway 9 already,” Villa said. “They’re up there on Weatherby.”

Friday, noon

Two infrared scopes aimed at Weatherby Canyon had detected no movement the night before. Parra returned to look for signs that the smugglers had come down the mountain. Two younger agents searched for an hour and found nothing.

Within 10 minutes of arriving, though, Parra picked up the footprints.

He tracked the sign on foot for several miles along the side of Weatherby until it disappeared. Sweat dripped from his face as he paused to take a swig from his water bottle.

“I’m leaning toward thinking they’re still up on top of those hills,” he said, lighting a Marlboro. “We were keeping this area very hot last night, and they could have stayed up.”

Later, Parra reconsidered when a nearby rancher reported that his dogs had barked loudly at 3 a.m."I don’t see how we would have missed them,” he said. “But the dopers must have been moving.”

Saturday morning

Tim Lowe, the day supervisor, dispatched two agents on ATVs to Weatherby.

A scope had been deployed there briefly the night before, “but they 10-3ed it,” Lowe said, using the code for terminating an operation. No one had been able to pick up the sign again.

Sunday afternoon

The exit for Steins Ghost Town on Interstate 10 leads to a cemetery of weathered crosses. Next to the cemetery, pieces of cloth and shoulder straps made of old blankets lay on the ground.

The drugs were gone, likely bound for Tucson and points west.

So were the smugglers, headed back to Mexico to collect their paychecks and pick up another load.

Back on the border, the day shift was out -- cutting for new sign.

scott.kraft@latimes.com