In all her years of tending sheep in the western reaches of the Navajo range, Lois Neztsosie had never seen anything so odd.

New lakes had appeared as if by magic in the arid scrublands. Instead of hunting for puddles in the sandstone, she could lead her 100 animals to drink their fill. She would quench her own thirst as well, parting the film on the water's surface with her hands and leaning down to swallow.

Despite the abundant water, an unexpected blessing, her flock failed to thrive. The birthrate dropped, and the few new lambs that did appear had a hard time walking. Some were born without eyes.

Lois' husband, David, wondered whether the sheepdogs were mating with their charges. A medicine man, he also suspected witchcraft. He tried to fight the spell by burning cedar and herbs and gathering the sheep around the fire to inhale the healing smoke.

The livestock were not his only worry. A mysterious sickness was affecting the couple's two youngest daughters.

Laura, born in 1970, had a weak right eye and was prone to stumbling. Arlinda came along the following year and developed ulcers in her corneas by age 5. A few years later, she was walking on the sides of her feet.

At the Indian Health Service hospital, doctors were mystified. Experts concluded that both girls suffered from a rare genetic disorder.

There was another possibility, but no one considered it until many years later.

No one connected the children and the sheep.

Tainted oases

In the mountains and mesas of the Navajo reservation, mining companies drilled tunnels in the sides of cliffs to extract uranium for the nation's nuclear weapons program during the Cold War. But in the red and ocher sands around Cameron, where deposits were shallow, the ore was blasted out of the plains, creating pits.

As demand for uranium eased in the late 1950s, the U.S. government allowed the companies to leave without filling in the craters. The pits collected snowmelt in the winter and runoff from summer torrents. The holes, some as deep as 130 feet, soon formed oases in the desert.

Lois grew to depend on them as she ranged far from home, covering as much as 10 miles in a day. At dusk, she often camped for the night. She got in the habit of filling and refilling a small container with her drinking supply as she moved from one "lake" to the next, watering her herd.

Every few weeks, the Neztsosies butchered one of the sheep. They ate each one down to the bones, which they sucked around the fire. They destroyed the lambs that could not walk.

Deformed animals were showing up in other sections of Dine Bikeiyah, Home of the People, as Navajos call their homeland. In areas around old mines, lambs and cattle developed shaking limbs, yellow eyes and white patches on internal organs that were discovered after slaughter.

Word of these strange developments did not reach the Neztsosies. Navajo families tend to live miles apart from one another. They prize their privacy. Local officials heard occasional complaints about damaged animals, but no one discerned a trend.

Baffled doctors

Arlinda, nicknamed Linnie, had that "funny walk," as her family described it. At the Indian Health Service clinic in Tuba City, Ariz., doctors prescribed Vitamin A for her eyes and gave her goggles to wear. Classmates teased her, so she stopped using them.

When she stopped taking her supplements, her Vitamin A levels remained normal — but her corneas did not improve.