"They're out here, but you've got to open your eyes," says Don.

Out here, north of the urban rush, rains have charged the North Sulphur River basin. Water scouring the channel and cutting creek banks can yield a fresh spread of fossils, ancient bones and human artifacts. And the Fagerstroms have come from Collin County to see what has turned up.

Maybe another beast?

Lying across an area long ago covered by an inland sea, the North Sulphur has long been a fossil collector's paradise. But 65 million years after the ocean withdrew, another inundation is in the works -- one that would end some of the tromping around.

In the Dallas area's endless thirst for new lakes, the Upper Trinity Regional Water District is seeking state approval to dam the river near the town of Ladonia and take 11,000 acres of rural Fannin County. About 65 miles northeast of Dallas, the proposed Lake Ralph Hall would provide water for Fannin County and the district's customers in Denton, Dallas and Collin Counties.

The dam would begin catching water 12 years from now at the earliest, the district estimates. Supporters say the lake, besides serving the faucets and lawns of a growing area, would stimulate the Fannin County economy. Others, such as the town of Flower Mound, the water district's largest customer, are questioning whether the $200 million project is needed. Environmental groups are calling for water conservation and reuse before new reservoirs. Some Fannin County landowners are organizing for a fight.

Fossil hounds don't want to say goodbye to this 10-mile stretch of the river. As a navigable waterway, the North Sulphur is open to public access. "There's something for every collector there is they want to go and get it," says Fred Ransdell, president of the Dallas Paleontological Society.

The river and creeks attract scientists and hobbyists, who have taken untold specimens to museums and home displays. Hundreds of species of marine plants and animals, many dating back 78 million to 80 million years, have been documented, as have remnants of life on land -- from arrowheads and spear points to mammoth bones and mastodon teeth.

In providing flood control for a river that sometimes runs dry, the proposed lake would supplant a failing project that put the North Sulphur on the fossil map. In the early 1930s, a drainage channel was built near the meandering river to reduce cropland flooding. The straightened path, however, quickened the river's flow and erosion, and untold acres of dirt have washed away. Originally 16 feet wide and 10 feet deep, the channel is now about 250 feet wide and 40 feet deep at the lake site. But the landowner's loss has been the fossil hunter's gain, as new pickings are exposed.

"You never know what you'll find," Don says as he and Jane round a bend in the creek. They chuckle about the wristwatch and dentures found in the river. The calf-deep muck grabbing at their rubber boots isn't quite so funny. "It's never been this muddy before, Dad," Jane says to her husband.

The Fagerstroms are among the river's regulars. After retirement, they moved to the town of New Hope. And living about an hour's drive from the river, they've been averaging two or three outings a week for the last dozen years. "How many things in life can you just enjoy and do what you want to and it costs you the gas to get there and back?" asks Jane. "It's something we can do together. Oh, and there's lots of exercise."

The two have been together most of their lives. They dated in high school, married in Minneapolis 53 years ago and moved to the Dallas area with their three children and Don's job as an aviation electrician. They started collecting rocks, turning to fossils after a first trip to the North Sulphur in the late 1970s. And after hunting in Kansas, Colorado, Utah and elsewhere, they say the river is more than just convenient. "When we come home, we say, 'Good. Now we can go to the Sulphur,'" says Jane. "It has such a vast amount of different things."

So do their yard, shop and home. Blocks of petrified wood from Utah fill two front flowerbeds. Piles of basalt, geodes and agates from Utah are among 22 tons of rock out back. "That's dinosaur droppings there," says Don, pointing to a pile of coprolite. Rocks, bones and fossils fill containers and shelves inside the shop. "Here's some enamel of mastodon teeth," Jane says.

Inside the house, a living room bookshelf holds 23 fist-sized vertebrae of an elasmosaur, a marine reptile. A jewelry case shows off more remnants. The big prize yawns in a room nearby. Behold the pieced-together skull and 80-toothed jaw of a TYLOSAURUS PRORIGER [pictured in the article - R]. The lizardlike reptiles roamed the world's sea and beyond until about 65 million years ago.

WHAT IS A TYLOSAURUS PRORIGER?
* The creature was one of at least five species of tylosaur, a large lizardlike marine reptile that lived in the world's oceans until about 65 million years ago.
* The oldest fossil specimen of a tylosaur, found in Kansas, is about 87 million years old. The largest, found in Europe, stretches over 55 feet.
* The beasts ate fish, marine birds and other mosasaurs.
* They were among the most common marine reptiles during the Late Cretaceous, 90 million to 65 million years ago.
Source: Mike Everhart, Oceans of Kansas Paleontology

Extending 5 feet 2 inches from stem to stern, the Fagerstroms' specimen, made up of bone and some fiberglass filler, is among the largest in North America, Mr. Everhart says. The couple unearthed the find three years ago and also have 65 vertebrae of what Mr. Everhart figures would have been a 38- to 40-foot-long animal.

Where the creek opens to the river, the couple wades through ankle-high water atop a base of gray fossil-bearing mudstone. With walking sticks in hand and folded stools riding on their backs, they tread thickly across mud, among gravel, up and down the ice-rimmed channel sparkling in midday sun. They feast on candy bars, protein bars and water with Don, 73, never getting off his feet and Jane, 71, resting briefly on her stool. And under a crystal blue sky, they may break the silence to praise the day or discuss the fine science of the search. "You keep your head down," says Don. "You can't be a bird-watcher and a fossil hunter."

More than six hours on the trail has left them a little tired and with little to show: some mosasaur bones, petrified wood and an arrowhead. "We've had good days and bad days," says Don, "but this was a terrible day." Homeward bound, he and Jane talk about why they will surely return. "It's the thrill of finding things that people haven't seen before or touched before," says Don. "And you get out and move around."

The loss of hunting grounds troubles collectors such as Dale Bordelon. The area's location, public accessibility and wealth of fossils and artifacts make it an educational resource worth saving, he says. "It's geography, chemistry, biology, geology, anthropology," says Mr. Bordelon, who bought 25 acres near the river so he and his three children could be close to the action. "And it's right in the back yard of the metroplex."

He knows that these traces of the past probably won't stop this lake for the future. And indeed, fossils and artifacts, while not ignored, typically don't halt lake projects, said Skipper Scott, an archaeologist for the Army Corps of Engineers. The corps regulates the damming of waterways. The Upper Trinity Regional Water District wants to develop a fossil park near the lake, said executive director Tom Taylor. Although the water would cover fossil fields, the loss should be balanced against the lake's good, he said. "Any public service that provides benefits takes land."

Mark McKinzie, co-author of a fossil guidebook to the North Sulphur, said "it will be a shame to flood" the river. A geologist, he also takes the long view that the Earth's climate, sea level and geology will keep changing. "Eventually, the lake will be gone. It's a man-made structure," he said. "Those fossils will be exposed again one of these days."