MANSFIELD, La.  They had to repeat the amazing number, $28.7 million, over and over, to make sure it was real and would not go away. Even then, the members of the De Soto Parish Police Jury  the county commission  could hardly believe it.

They laughed, rocked back in their chairs, shook their heads, stared at the ceiling and muttered oaths to each other. “We have  $28.7 million,” said the president, Bryant Yopp, to settle the matter, definitively if still incredulously. It was nearly one and a half times the parish’s entire annual budget.

A no-holds-barred, all-American gold rush for natural gas is under way in this forgotten corner of the South, and De Soto Parish, with its fat check from a large energy company this month, is only the latest and largest beneficiary. The county leaders and everyone around them, for mile after mile, over to Texas and up to Arkansas, in the down-at-the-heels city of Shreveport and in its struggling neighbors, suddenly find themselves sitting on what could prove to be the largest natural gas deposit in the continental United States.

Already, several dozen people who own parcels of land over the field are becoming instant millionaires as energy companies pay big money for the mineral rights to the gas, which like other energy sources is worth far more than it was last year. Jalopies are being traded in for Cadillacs, plans for swimming pools are being hatched in rusty trailers, and the old courthouse here is packed to the rafters day after day with oil company “landmen” (and women), whose job it is to frantically search the record books for the owners of the mineral rights to land that has become like gold.