JOSEPH, Ore. — Geologists come here from around the world to look at the textbook-perfect glacial moraines rising above Wallowa Lake, but what they increasingly see is a proliferation of weeds growing on the symmetrical rocky knolls.

One of the most prominent is a spiny, flowering variety called spotted knapweed that elk refuse to eat. The weed can trigger soil erosion, in turn causing the gradual slide of the moraines into the gemlike 280-foot-deep lake.

Local volunteers calling themselves the Wallowa County Weed Warriors climb the 950-foot-high moraines on weekends and evenings to pull pesky knapweeds out by the roots.

"We are fighting alien terrorists," said geologist Ellen Morris Bishop, an organizer of the 2-year-old group and author of "In Search of Ancient Oregon." "These plants are hostile to humans, and they basically armor-plate a landscape so it's theirs and not ours anymore."

Coffee-shop talk here often centers on rising cougar numbers and the possibility that gray wolves might again become part of life in this northeastern corner of the state. But Wallowa County's most costly problem may be invasive weeds, land managers say.

Oregon lists 105 noxious weeds, but a mere 21 of those varieties cost taxpayers $83 million a year — largely in grazing and timberland losses, said Tim Butler, manager of the Oregon Department of Agriculture's noxious-weed program.

The state's most notorious invasive weed probably is Scotch broom, he said. Found on 7 million acres of Western and Central Oregon, it has spread as far east as Pendleton and alone accounts for $47 million a year in lost revenue, Butler said.

Small infestations of noxious weeds have taken hold in a quarter of the 652,488-acre Hells Canyon National Recreation Area in Wallowa County, and they could grow into large infestations without attention, said Leigh Dawson, U.S. Forest Service noxious-weed coordinator in Enterprise.

One of the Forest Service's biggest concerns is stopping the spread of yellow star thistle into Hells Canyon. It can make hiking an ordeal because of its needle-sharp thorns. Another concern is leafy spurge, which exudes a sap that can cause temporary blindness and boils when it comes in contact with eyes and skin.

Elsewhere, Dalmatian toadflax sometimes grows 4 feet tall in Hells Canyon's draws, and Japanese knotweed clogs streamside areas. Common bugloss, rush skeletonweed, whitetop and Medusa head are other havoc-wreaking varieties.

Yellow star thistle chokes 45 miles of Idaho's Salmon River corridor, in some spots from river to rim tops, and appears to be moving toward Hells Canyon, said Lynn Danly, rangeland specialist with the U.S. Bureau of Land Management in Cottonwood, Idaho. She watched the Salmon River's Rattlesnake Ridge area go from native plants to "a sea of yellow star thistle" in nine years.

That's a scary proposition in Wallowa County. If the infestation reaches Hells Canyon, the county stands to lose habitat for wildlife and birds and suffer unprecedented soil erosion.

Wallowa County has joined a Tri-State Weed Management Area with Idaho and Washington. It also helped form the Wallowa Canyonlands Partnership with various local and federal agencies to come up with a weed management plan.

"The funny thing is, a lot of these weeds started out with grandmothers bringing them in their gardens," Dawson said. "A lot of them still can be found in ornamental seed catalogs. Dalmatian toadflax is a beautiful weed."

In another twist, the invasion here seems to have begun in earnest after the Forest Service removed domestic sheep from Hells Canyon in 1996 because they carry a strain of the pasteurella disease that kills wild bighorn sheep.

The domestic sheep munched on grasses that now can tower 5 feet tall in the canyon. Uneaten grasses cure to tinder dryness by late summer and can carry hot, fast-burning wildfires faster than a person can run. Wildfires cause soil disturbances that are an open invitation to weeds.

The Eastside Complex wildfire in August 2000 blackened 118,597 acres, destroying stands of timber hundreds of years old that extended up and down the sides of Hells Canyon.

"I love bighorn sheep, I do," said Mark Porter, who works for Enterprise-based Wallowa Resources, a nonprofit community-based forestry organization that does contract work for the Forest Service. "But when you manage for one thing you can lose your perspective. ... We need to manage that whole system."

Among possible solutions is using a miniature variety of longhorn cattle called Corriente in the canyon as a "prescription" grazing tool, Porter said. He also likes the idea of combining insect foes of weeds and chemical herbicides.

Arleigh Isley of John Day, a former Wallowa County commissioner and retired Oregon State University extension agent, recommends introducing a mix of sheep, cattle, horses, mules and goats to graze on the weeds and summer grasses.

Some studies suggest bighorn sheep wouldn't risk catching pasteurella if individual bands were kept to no more than 100 animals, he said.

Fewer than 2,200 cattle graze during part of each year in the Hells Canyon recreation area now.

The Forest Service's Dawson believes climate factors and the various ways people accidentally transport seeds into the canyon play a larger role in the spread of weeds than the removal of domestic sheep. "I think that is a stretch," she said.

"You have so many other factors," Dawson said. "Nature is very complicated and interwoven."

Winning government approval to allow more grazing in the canyon would be a "massive undertaking" and take a long time to happen — if ever, she said.

In the meantime, the Forest Service will rely on weed-pulling teams, herbicides and insects to attack the interlopers — and hope that those can whack the weeds back into submission.