SHENANDOAH NATIONAL PARK, VA. -- The trail was steep enough to turn younger legs to jelly, but Alice Ruddiman wasn't complaining. Up, up, up she went, stepping carefully over loose rock, bracing against tree limbs, skirting patches of poison ivy and stinging nettle.

In less than a mile, the 77-year-old retired office worker had climbed nearly 1,000 feet. "It's my only real form of exercise," she said, which is a little like John McEnroe allowing that he sometimes gets in a set or two of tennis.

Walking is more than a pleasant diversion for Ruddiman and others in the Potomac Appalachian Trail Club, a 3,300-member organization devoted to the care and appreciation of the sinuous 2,100-mile Georgia-to-Maine footpath that gives the club its name.

This week, the Appalachian Trail -- or A.T., as it is known to the backpack set -- is celebrating its 50th anniversary, a tribute as much to the devotion of its caretakers as to the trail itself.

"It's like Mount Everest," said Rima Farmer, who works for the Appalachian Trail Conference in Harpers Ferry, W.Va. "We may not ever visit it, but knowing that it's there makes us all richer."

Conceived in 1921, the trail was completed by the Civilian Conservation Corps Aug. 14, 1937. Stretching from Mount Katahdin in Maine to Springer Mountain in Georgia, the trail follows the ridgetops through 14 states, eight national forests and six national parks. Half the nation's population lives within a day's drive of its route. Though millions have walked sections of the trail, only 1,500 are believed to have hiked the entire route, a six-month trip.

Few public resources owe so much to volunteers. Though nominally under the control of the National Park Service, the Appalachian Trail and its numerous spurs are maintained by 31 clubs, each responsible for a portion.

The Potomac Appalachian Trail Club, one of the largest, takes care of 200 miles between the Susquehanna River in Pennsylvania and Rockfish Gap at the southern end of Shenandoah National Park.

The club assigns specific sections -- ranging from 2 1/2 to five miles -- to individual members, who tend to them like some people look after their gardens.

Bill Hutchinson, a retired Foreign Service officer, visited his section five times a year for six years, until arthritis forced him to hang up his shears.

"It's a lot of hard labor," said Hutchinson, 70, describing the tasks of clearing brush, sawing fallen trees -- power tools are forbidden -- and digging trenches for water runoff.

According to the standards set forth for the trail, brush and tree branches must be cleared to a width of four feet and a height of eight feet.

"The idea is to keep it clear for backpackers," said Hutchinson. "Some of them are tall."

Carol Flint sounds like a doting aunt when she talks of her section, a side trail in the park called Little Devil's Stairs. "You develop a great fondness," she said, adding that she has tended the same path for 17 years.

People who like nature tend to like each other, and it would be hard to find a friendlier group than the one that assembled Wednesday morning at the Oakton Shopping Center for the club's weekly outing.

Mostly retired people, they have hiked together around the region and, in some cases, around the world. "Pat, Jack and I met when my husband and I did the towpath from Cumberland to Washington," said Donna Boies.

Five members of the Wednesday group just got back from the Swiss Alps.

Most of them long ago lost track of how many miles they have hiked on the Appalachian Trail. "I've never tried to estimate it," said Hutchinson. "We hike the same parts again and again."

Wednesday's destination was Big Devil's Stairs, a side trail in the northern end of the park. Leaving their cars on a narrow country road at the park's edge, the hikers nimbly scaled a fence and set off briskly into the woods.

Bill Taft, 72, observed that it is quite remarkable that the same people keep hiking year after year. "Only one or two people have had to opt out because of operations or knee problems," he said, adding that he missed a few hikes after he fell into a creek and hurt his foot.

During a stop for lunch, one member said he would not be able to make an upcoming hike because of an appointment at the cardiac clinic. But he indicated that he would be back soon after that.

Naturalists one and all, the hikers shared stories of things they had encountered in the wild: bear excrement ("It looks like a horse's, only it's more liquid"); rattlesnakes ("They're practically endangered, don't you know?"), and spiders ("It was the kind with the armored abdomen").

After lunch, Dick Wightman, 62, decided it would be a good idea to climb a nearby peak to help him prepare for a 450-mile hike through France. "Charge ahead, boys," Alice Ruddiman said, jogging to catch up.

After they got back to the cars, everybody had some beer while Jack Meiners played his harmonica. Lu Beale congratulated her dachshund Josie for completing the nine-mile hike without having to be carried.

Then the hikers gathered around a map of the Appalachian Trail and picked next week's destination.