The clear, flowing Smith River is a life force in the northern corner of California, where the locals keep a sharp eye out for threats to the pristine water and thriving fish.

That would explain why the folk who live along the river in Del Norte County nearly jumped out of their britches when they learned about a proposed nickel mine along a major tributary of the Smith, the last major river without a dam left in the state.

A London mining company has applied to the U.S. Forest Service to begin exploratory drilling over thousands of acres of forest lands, including Baldface Creek, in Curry County, Ore., which flows into the Smith and helps maintain one of the most abundant natural salmon runs in California.

Steelhead trout, chinook and coho salmon spawn in both Baldface Creek and Smith, a National Wild and Scenic River that also provides Crescent City and the surrounding communities with drinking water.

"Locating a strip mine in the headwaters of the wild and scenic Smith River is like putting ice cubes made with toxic waste in your favorite drink," said Grant Werschkull, the executive director of the Smith River Alliance, in Crescent City. "It's completely outrageous."

Toxic pollutants known

Nickel mining is well known for leaving environmental scars, including several superfund sites. This type of hard rock mining is the largest source of toxic pollution in the United States, according to the U.S. Environmental Protection Agency.

The proposal by the Red Flat Nickel Corp. is to begin drilling above Baldface Creek southeast of the Kalmiopsis Wilderness in the Klamath Mountains of southwest Oregon to determine whether a full-scale mining operation would be economically feasible. It is one of several large mining claims by the company on nearly 10,000 acres of sensitive watershed lands in the area, including a connected tributary called Rough and Ready Creek, which flows in the opposite direction from Baldface into the Illinois River.

An attorney representing Red Flat could not be reached for comment, but federal officials said construction of a mine is still a long way off.

Sets off ruckus

"It's a plan of operation for exploratory drilling," said Virginia Gibbons, the spokeswoman for the Rogue River Siskiyou National Forest, the land management agency in charge of the process. "It doesn't mean there is going to be a mine there."

The plan has nevertheless created a major ruckus among politicians, homeowners, fishermen, environmental groups and American Indian tribes, who have all expressed major concerns about the proposal.

Environmentalists fear toxic runoff just across the state line will pollute downstream locations, including the Smith River National Recreation Area and Redwood National and State Parks.

Glen Spain, the northwest regional director for the Pacific Coast Federation of Fishermen's Associations, said a mine in that location could undo the millions of dollars spent by the state and federal governments on restoration work in the river system.

"It's astonishing that this kind of thing still happens," Spain said. "Trying to put any major mine in the middle of the headwaters of any major salmon river is a recipe for disaster."

Eugene Palazzo, the city manager for Crescent City, said he is keeping a close eye on the process.

"There is certainly concern because the water we service our community with we get from the Smith River," Palazzo said.

Easy to stake claim

Problem is, there may not be much anybody can do to stop the company from putting in a mine. For one, the mine would be in Oregon, not California. Then there is the General Mining Act of 1872, which gives mining companies almost carte blanche to stake claims and dig for minerals.

The law, approved during the presidency of Ulysses Grant, codified the informal system of acquiring and protecting mining claims on public land by prospectors in California and Nevada starting during the Gold Rush. It says, in essence, that all citizens 18 years or older have the right to make a claim on federal land and extract minerals for a nominal fee.

Gibbons said the national forest agency is required to process the operation plan, which was first submitted in October 2012.

"We're bound by that 1872 mining law to respond when a plan of operation is submitted. We can't choose not to respond," she said. "We are required to process that request (and) to move forward with a submitted plan of operation."

Groups pressure lawmakers

The Smith River Alliance, Spain and tribal representatives at the Elk Valley Rancheria are urging Oregon Rep. Peter DeFazio and U.S. Sens. Ron Wyden and Jeff Merkley to resubmit previous requests they have made to the Obama administration to withdraw the land from mineral development.

"We have steadily urged protection for these threatened creeks and call on the administration once more to act now and prevent mining activities from damaging critical habitat for endangered salmon and steelhead," the three politicians wrote to Secretary Sally Jewell last year.

Forty local, regional and national organizations in California and Oregon are urging congressional leaders to introduce legislation to withdraw the streams from the mining law.

The U.S. Forest Service is consulting with tribal leaders about the Baldface Creek proposal and is expected to release an environmental analysis this summer, but without government intervention the final decision will be made by an overseas corporation.

Peter Fimrite is a San Francisco Chronicle staff writer. E-mail: pfimrite@sfchronicle.com Twitter: @pfimrite