The bright yellow signs on U.S. 285 are the first indication that things aren't right in Carlsbad.

"US 285 south subject to sinkhole 1,000 feet ahead," motorists are warned.

But there is little other evidence that in southeastern New Mexico's oil country, a giant cavern sits beneath the earth, ready to swallow part of the highway and possibly a church, several businesses and a trailer park.

The cavern was formed over three decades as oil field service companies pumped fresh water into a salt layer more than 400 feet below the surface and extracted several million barrels of brine to help with drilling. State regulators flagged it as a potential danger after concluding that it was similar to two wells northwest of Carlsbad that collapsed without warning last year.

Over the past few decades, communities in Texas, Kansas, Michigan, Canada and Europe learned of similar underground danger only after cracks appeared and the ground began to sink. Regulators are trying to determine how to prevent future collapses by better managing a practice that's used throughout the world.

Most brine wells operate far from homes and businesses, but Carlsbad's is unique because it is in a population center — and could prove potentially disastrous.

"It would be a mess. It would be like a bomb going off in the middle of town," said Jim Griswold, a hydrologist with the New Mexico Oil Conservation Division.

The city council and the Eddy County Commission declared a state of emergency Thursday, the first step to free state and federal funds that could be used to figure out a way to stabilize the cavern.

"The public's been warned," Carlsbad Mayor Bob Forrest said. "We've had a heads up, and for us as elected officials to sit here and do nothing is political suicide. We want to move forward."

The city of about 26,000 residents knows caverns well. It is home to Carlsbad Caverns National Park, a network of some of the largest natural caverns in North America, where tourists can see both delicate calcite formations and towering stalagmites.

Alarms set up to monitor

But this man-made salt cavern has residents nervous.

Officials have set up a monitoring system that takes readings from tilt meters and pressure sensors every two seconds and averages them to determine whether there are changes drastic enough to trigger alarms. The alarms are expected to give authorities several hours to evacuate people in advance of a cave-in that could span anywhere from 200 to 500 feet, Griswold said.

I&W Trucking, the oil field service company that owns the site where the cavern is located, contends the state is overreacting because of the previous collapses on state land and criticized the Oil Conservation Division for not doing more tests to establish the size of the brine cavern before forcing it to plug the well.

The agency hired independent consultants to determine the size and shape of the cavern and the risk of collapse.

Eugene Irby, whose family owns I&W Trucking, said the company has always followed the rules and performed annual pressure tests on the cavern. Had the cavern been that unstable, he said, it would have already collapsed, given that more than 2 million pounds of water and heavy trucks were on the surface every day.

"I went to work there every day," Irby said. "I would walk the yard at times and if there were cracks in the ground I would have seen them. There's none."

I&W has given up the brine operation, emptied its tanks and moved down the road.

Nervous neighbors

But trailer park residents Cookie and Ellie Fletcher have been left to wonder what they will do if a sinkhole opens on the other side of the chain-link fence. They are on fixed income and said they could never afford to move.

"It's a nightmare," Ellie Fletcher said, motioning to the wells and tanks in the distance. "I would like to forget about it, but I can't forget about it because it's right there."

It doesn't help that curious friends and acquaintances bombard the Fletchers with questions about the sinkhole each week at church.

At the Circle S Feed Store, next door to the well site, store owner Wally Menuey doesn't need the repeated requests from customers to look at the hole, even though none exists yet.

Menuey said the first thing he looks for when he rounds the corner into the parking lot each morning are the tanks next door. If they're still standing, he knows it's safe to continue on to work. Still, he said, structural cracks have formed in the store.

"It makes you wonder," he said.

The potential sink hole wouldn't just swallow parts of the town. Potential crop damage could total $100 million.

No one knows when the cavern might collapse. But the mayor and other city officials are worried about getting the money they need to tackle the problem in time to stop the worst from happening. State officials said parts of the ground above the well are already heaving while other parts are sinking.

"The clock is ticking," said Jim Goodbar, a senior cave and karst specialist with the Bureau of Land Management.