LAS VEGAS >> The U.S. Air Force is giving an ultimatum to owners of a remote Nevada property now surrounded by a vast bombing range including the super-secret Area 51: Take a $5.2 million “last best offer” by Thursday for their property, or the government will seize it.

The answer: No, at least for now.

The owners, who trace their mining and mineral claims to the 1870s, include descendants of a couple who lost their hardscrabble mining enterprise after the Air Force moved in in the 1940s. Nuclear tests then began in 1951, their mine mill mysteriously exploded in 1954 and they ran out of money to seek reparations from the government in 1959.

“What they really want to buy is our property, our access rights and our view,” said Joseph Sheahan, 54, who has led the fight with his cousin, Barbara Sheahan Manning, on behalf of about 20 property co-owners. Both live in Henderson, Nevada.

“We prefer to keep our property, but it’s for sale under the right price at the right conditions,” Sheahan said. “Why don’t they ask themselves what it cost my family over the years in blood, sweat, tears and money?”

The two sides are far apart. And they know condemnation proceedings would lead to a “fair market value” determination that could end up in court for a long time.

The federal government gradually encircled the mine property — totaling fewer than 400 acres — northwest of Las Vegas, making it a private island reachable today only by passing armed guards at security gateposts. The surrounding secure 4,500-square-mile reservation for nuclear testing, military training and other research is almost twice the area of the state of Delaware.

“The land has become an increasingly greater safety and security risk as demand for test and training opportunities have increased,” the government said in an Aug. 28 news release describing the final offer.

Today, Groom Mine overlooks Groom Lake, a site so secret that Col. Thomas Dempsey, a Nellis Air Force Base commander, would only refer to it on Friday as “one of many remote locations within the Nevada Test and Training Range.”

“Nothing you can look up in any Air Force naming convention refers to Area 51,” added Jennifer Miller, deputy assistant Air Force secretary for installations.

But check the Internet or watch TV’s “X-Files” and Area 51 and Groom Lake evoke tales of top-secret aircraft research and testing, CIA programs and maybe extraterrestrials. The Triple-A baseball Las Vegas 51s even poke fun at the legend, with the team name and a mascot character named Cosmo.

Sheahan family members consider themselves good neighbors and patriotic Americans, with generations of decorated military members, Manning and Joe Sheahan said. They don’t tell what they’ve seen.

But Manning, 59, remembers the tales handed down during decades on the porch of a rustic home overlooking Groom Lake.

“We didn’t have much more than a transistor radio and a deck of cards, and no indoor toilet,” she said. “Our grandparents told us the stories.”

For more than 70 years, since the U.S. government moved to that part of southern Nevada, “they have completely disregarded our constitutional rights,” Manning said.

She photographed records at the Lincoln County seat of Pioche showing the first two Groom Mining District mineral patents, filed in May 1876, were signed by President Ulysses S. Grant. With various additions over the years, the rights grew to include six patented claims and 15 unpatented claims.

Sheahan family forebearers mined lead and silver and other minerals for half a century before World War II and the Cold War created an urgent need for a remote place to test nuclear weapons. That brought the government, the military and mushroom clouds to the site some 100 miles northwest of what is now Las Vegas.

The demise of the mining enterprise is told in a 1959 letter from grandparents Daniel and Martha Sheahan to then-U.S. Attorney General William P. Rogers. Radioactive fallout from nuclear tests and the lack of a mill to process ore were to blame, they said. They also blamed disagreements with their own lawyers.

Partly for that reason, Joe Sheahan said, the owners haven’t hired attorneys for the current fight with the government. He said several owners aren’t Sheahan family members.

Manning said her father, Daniel “Bob” Sheahan and an uncle, H. Patrick Sheahan, put the value of the property at some $13.6 million in a May 1986 letter sent to the Air Force as part of an environmental study.

Miller, the Air Force official, said government estimates for property and mineral rights, after assessments in the 1980s and 1990s, were between $1 million and $1.2 million.

Taxpayer money is at stake. But the pending offer was stretched to $5.4 million in an effort reach an amount “reasonable prudent and in the public interest,” Miller said.

“The payment cannot result in a windfall to the owners,” she added.