BRIDGEPORT - For thousands of U.S. Marines, the road to Afghanistan goes through an isolated training facility in the Eastern Sierra where they share the rugged Humboldt-Toiyabe National Forest with civilian hunters, backpackers and skiers.

On a recent weekend, several hundred Marines were on an overnight march to test their land navigation, communication and outdoor survival skills. As they returned to base camp Sunday morning, hunters dressed in orange vests were driving up the mountain in hopes of bagging deer.

The two groups exchanged courteous waves: one using the mountains to train for war, the other for weekend recreation.

Col. Norman Cooling, an Iraq and Afghanistan combat veteran who runs the Marine Corps Mountain Warfare Training Center here, notes with some amusement an oddity in the Pentagon's agreement with the U.S. Forest Service: Civilian hunters can use live ammunition but Marines, except in designated ranges, are restricted to blanks.

In the last year, 13,541 Marines, sailors and foreign troops have trained at Bridgeport, an increase of 238 percent over the previous year. More increases are expected.

As the U.S. military trains to fight at medium and high altitudes in Afghanistan and other potential hot spots, "no other military venue in the nation can replicate these conditions better than here in the Eastern Sierra," Cooling said.

Marines train on 46,000 mountainous acres owned by the federal government, 20 miles outside Bridgeport (population 900) just north of the Yosemite Valley - all set in a postcard-beautiful region of tall trees, the fast-moving Walker River, thick winter snow and terrain favored by deer, bears and cougars.

State Highway 108 runs past the training center's buildings in Pickel Meadow to the Sonora Pass, at 9,624 feet, the second-highest highway pass through the Sierra. In the spring and early summer, the meadow and mountain slopes are brilliant green; in fall, the aspens turn golden and then bright orange.

The Marines have had a training center here since the Korean War, but the war in Afghanistan, with its mountains and spread-out population, has given the remote facility a new significance.

Marine Staff Sgt. Thomas Davis will soon be in Afghanistan, working with rural villagers to win their support for the U.S.-led war against the Taliban. Gunnery Sgt. Brad Lenox will be building expeditionary airfields, allowing the United States to quickly move troops and supplies in a region with few roads.

And Sgt. Nicholas Heier's engineering battalion could be in Afghanistan to provide "sustainability, mobility and counter mobility," which includes hunting for roadside bombs before they can kill U.S. troops. "You can't get this terrain anywhere else," Heier said.

Bridgeport is meant to prepare Marines for Afghanistan's cold, snowy winters; rugged landscape where communication is difficult; and high altitudes where breathing is labored and the trajectory of bullets is difficult to gauge. To enhance the realism, various areas are given names meant to sound Afghan.

"If you can move, shoot and communicate in the mountains, you can do it anywhere," said Maj. Urbano Cruz, the officer in charge of training.

The Marine Corps has expanded training eastward beyond the national forest into flatlands controlled by the Bureau of Land Management. A 68-mile overland convoy route through Lucky Boy Pass to the Army depot in Hawthorne, Nev., prepares Marines for the roadside bombs and sniper attacks they are likely to encounter in Afghanistan.

At Bridgeport, Marines receive instruction in avalanche survival, cold-weather medicine, the use of donkeys and mules as pack animals and how to adjust for thin air and tricky winds when aiming a sniper shot. There are live-fire ranges - away from the areas where civilians are permitted.

Many of the courses are for small groups of Marines selected by their superiors. Others are for companies of 100 Marines or more.

Eight times a year, entire battalions (each with 800 to 1,200 Marines)cometo Bridgeport for a 21-day exercise called Mountain Warrior. In the winter, two days are added for snowshoe instruction.

The Dutch and British military send troops to Bridgeport for training.

The Bridgeport curriculum includes Afghan émigrés playing the part of villagers, some friendly, some hostile, many incredulous. Faux villages are set up to add to the realism, although Forest Service rules dictate the structures can be left up for only a few days at a time.

Many of the Marines from the 4th Civil Affairs Group are veterans of similar missions in Iraq. Afghanistan will be more difficult, they agreed.