One hundred years after Rock Creek Park was created, the largest natural urban park in the world is known to most Washington area residents primarily as a scenic commuter route and a playground for joggers and bicyclists.

The linear swath of rugged greenspace that stretches from across the Maryland border to the Potomac River was created by a bold act of Congress in 1890, and park officials are planning to mark its centennial with a daylong festival on Sunday.

But park officials say this national treasure of nearly 3,000 acres, with a remarkably low crime rate, remains largely unknown and underutilized. Although 70,000 people drive through it daily and 12,000 joggers and 1,000 cyclists crowd its paved paths each month, the National Park Service counts a monthly average of only 1,100 walkers in the open areas. And there are too few to count on the hiking trails.

Yet along the 13 miles of narrow footpaths that crisscross the forest is the real park, an unspoiled wonderland of tall trees rich with woodland birds and other wildlife, sweet-scented wildflowers and the magical sound of water rushing over the stones of shallow Rock Creek.

On these foot trails, Ranger Cindy Donaldson has found three sites where, on a weekday morning, the dense forest blots out the outside world.

"This is my favorite spot," she said, pausing at a bend in the Valley Trail east of Riley Spring Bridge. "There is nothing to hear but the sounds of the park."

Closer to the creek near a picnic area, Alexander Wolf, Jr. and Marjorie Fix were walking Fix's dog, Torri. Wolf, who proclaimed himself a lifetime fan of the park, said his grandfather, Max Weyl, made his living painting pictures of the park at the turn of the century.

"I have one over my mantel," he said. "It's a beautiful scene . . . . looks very much like the park today."

The appeal of the park is that it is virtually unchanged and most of its acreage is in its natural state, said Mac Palmer, assistant chief of maintenance for the park and a 31-year employee of the National Park Service.

The exceptions are the picnic areas, the tennis courts, the golf course and 200 garden plots established during World War II.

"Eighty-five percent of the park is natural," Palmer said. "That is far greater than any other large urban park."

Efforts to keep the park as natural as possible have led to the return of deer, which left decades ago for suburban woodlands. Resource manager Bob Ford said the herd numbers about two dozen and is growing.

Ford said the park continues to be home to about 1,200 species of plants, including the now-rare northern maidenhair and rock polytody ferns.

It also is home to a large variety of birds, documented each Christmas since 1948 by the Audubon Naturalist Society.

Park police said the park is one of the safest places in the city, although they warn that night is no time to be there because there is little lighting.

Among Palmer's duties, however, is keeping track of two automatic counters on park roads, which he said show regular use to be well over capacity.

"Our major concern is {that} the roadways through the park have become commuter routes," he said. "Our mission is to give people a place to get away from the hustle and bustle, not to be a part of it."

The fast-paced traffic has gotten the attention of the Park Police.

"We use radar enforcement just about every day," said Lt. Henry Burburich, commander of the park substation. "I get a stack of tickets in here three inches high every time we go out."

On roads marked 25 mph and 35 mph, "some of the violators get up to 50 or 60 miles per hour," he said. "If we don't catch them, a tree or the creek will."

A century ago, no one thought in terms of commuters. The original intent, according to the Congressional act, was for the land to be "perpetually dedicated and set apart as a public park or pleasure ground for the benefit and enjoyment of the people of the United States."

The first bill was introduced in 1867, but was opposed by lawmakers from western states who saw no benefit to their constituents.

Nothing more happened until 1883, when the anticipated cost of the land blocked action. Seven years later, after much behind-the-scenes maneuvering by key senators, the bill creating the park finally passed and was signed into law by President Benjamin Harrison on Sept. 27, 1890.

It was a park on paper only. More than four years would pass before land was purchased and another three until construction began.

At the time, the creek had become an open sewer because of unregulated building nearby. A century later, raw sewage still spills into the creek when storm drains overflow. Park officials warn that it is unsafe to swim in the polluted water.

A newer problem is exotic pest plants such as English ivy, Asian bittersweet and porcelainberry introduced by well-intending neighbors who dump yard waste containing the pesky seeds in the park. The ivy has spread across some of the forest floor, choking out fawn lilies and spring beauties, while the other vines are growing up and over native trees and slowly smothering them.

Ford worries that the battle against the tenacious vines will be lost because of tighter budgets that include no funding for extra help next year to cut them back and discourage new growth.

But even the ravaging vines go mostly unseen, said Al James, recreation chief for the park, who said most of the park's visitors stay in the open areas.

"We have plenty of room for more people to walk in the park and come see what we have," he said. "Most people don't realize they have a national treasure at their back door."