Particularly toxic were the "hot" houses built with radioactive debris.

In every corner of the reservation, sandy mill tailings and chunks of ore, squared off nicely by blasting, were left unattended at old mines and mills, free for the taking. They were fashioned into bread ovens, cisterns, foundations, fireplaces, floors and walls.

Navajo families occupied radioactive dwellings for decades, unaware of the risks.

Over the years, federal and tribal officials stumbled across at least 70 such homes, records show. The total number is unknown because authorities made no serious effort to learn the full extent of the problem or to warn all those potentially affected.

After years of delay, they fixed or replaced about 20 radioactive houses and then walked away from the problem. Navajos continued to use mine waste as construction material, and the homes were passed down from one generation to the next.

Not until 2000 did the Holidays learn that their hogan was dangerous. By then, the couple had raised three children and sheltered a host of other kin while the uranium decayed. The resulting alpha, beta and gamma rays were invisible; the radon gas was odorless. But the combination greatly increased the chance of developing fatal lung cancer, according to a radiation expert who sampled air in the hogan.

"It brings chills when you're told that your house is like this," said Mary Holiday, now in her early 70s. "All the years that you've lived here," she said, her voice trailing off.

Unsuspecting, she had gone about her chores in the Navajo way, clad in the customary velveteen blouse, long skirt, thick socks and dusty shoes. She chopped wood for the stove, cooked tortillas and brewed tea. She set up her loom to weave rugs under a juniper tree while the grandchildren played dress-up for hours inside the old hogan.

By the time of the discovery that now torments her, she had lost her husband, Billy Boy, to lung cancer and congestive heart failure. He didn't smoke, but he'd worked in uranium mines by day and slept, unknowing, in the equivalent by night.

Her grandnephew, too, would soon die of lung cancer, at age 42. He had neither smoked nor mined. But he had lived in the hogan for three years as a teenager.

The dwellings in the Holiday family compound faced east toward dawn, in accordance with Navajo tradition. Behind them loomed the mesa, with a pale green uranium stain that started at the old mine and pointed down the cliff.

'Where is our guardian?'

More than 180,000 people live scattered across the region bounded by the Navajos' four sacred peaks. More than a homeland, it is their holy land. The tribe's creation stories are set here, among the painted deserts, ponderosa highlands and layered sandstone cliffs.

The U.S. government appealed to both Navajo patriotism and self-interest when it asked the tribe to open its land to uranium exploration in the 1940s. The mining would aid the American war effort and provide jobs, federal officials said.

Some of the mining companies were conglomerates like Kerr-McGee Corp. Some were small like A&B Mining, a Utah firm that was the last to mine the mesa near the Holidays' hogan.

Early on, federal scientists knew that mine workers were at heightened risk for developing lung cancer and other serious respiratory diseases in 15 or 20 years. Many did, and eventually their plight drew wide attention. In 1990, Congress offered the former miners an apology and compensation of up to $150,000 each.

But pervasive environmental hazards remained.

Starting in the late '50s, government scientists and inspectors had written memos and journal articles calling attention to the dangers posed by open mines and exposed tailings.

But the warnings failed to spark vigorous action. Pleading lack of funds, officials at the Environmental Protection Agency and the Indian Health Service dodged responsibility, declining to study the health threats comprehensively, much less eliminate them.

Navajo leaders tried sporadically to force federal action, usually without success. On occasion, they withheld information about uranium-related dangers from their own people, reasoning that there was no point stirring up fear if there was no money for a solution.