BLANDING — In the early morning darkness on Labor Day, officer Corey Workman pulls his patrol car behind a blue Dodge Durango with Arizona plates he clocked at 10 mph over the speed limit on the town's main drag.

Workman asks the driver to step out of the car to answer a few questions.

The man identifies himself as Jesus Espinoza. He says the vehicle is a rental, which Workman finds strange given the ornate mermaid license plate frame. Espinoza says he's headed to Monticello from Phoenix to help a friend repair a car. He identifies the woman in the front seat as his girlfriend.

The Blanding officer turns his attention to the woman, who says she is Espinoza's wife, Josefina. She tells him the couple is headed to Salt Lake City. Workman asks if there are any illegal items in the car. She shakes her head and looks increasingly nervous. She and Espinoza deny possessing any drugs.

Workman finds out both are undocumented immigrants from Sinaloa, Mexico.

With permission, Workman, Sgt. Cal Black and officer Darren Shumway and a search dog named Kiwi go through the Durango. They find $1,700 cash and a handgun, which is illegal for non-U.S. citizens to possess.

Police handcuff the couple. Espinoza is stoic; Josefina quietly cries. Though convinced the pair are concealing drugs, the searchers find none. They release them but keep the gun.

An hour later and miles up the highway, Workman and Black help Espinoza fix a flat tire.

Such is a night on Utah's main corridor for illegal immigration, human smuggling and drug running.

Hundreds of mostly Mexican nationals crammed into shoddy vans, SUVs and even U-Haul trailers pass through remote San Juan County in the state's southeastern corner each day.

Blanding police officers and Utah Highway Patrol troopers routinely pull them over, usually for minor traffic violations. But beyond that there isn't much they can do.

"We just cite 'em, collect bail and kick 'em down the road," Blanding Police Chief Mike Halliday said.

UHP Sgt. Rick Eldredge, who patrols the county's more than 500 miles of highway, said, "It's like trying to stop a river with a shovel."

U.S. 191 is a major route for undocumented immigrants making their way from Mexico via Arizona. Most are headed to I-70, then east to Denver and points in the Midwest.

Just this week, a minivan crammed with 16 occupants headed to Denver rolled on U.S. 191 near Moab. A woman from Mexico was killed and the others, mainly from Mexico and Guatamela, were injured, several of them critically. It's unknown how many were undocumented.

In a two-hour period early on a summer morning, Eldredge says he stopped vehicles containing 120 illegal immigrants, including a U-Haul truck jammed with 29 people. Most are men, though he occasionally comes across families.