"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.

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