The stone bridge at the heart of the new two-acre restoration of Dumbarton Oaks Park, which adjoins Dumbarton Oaks above. (Adrian Higgins/THE WASHINGTON POST)

I found myself on a steep hillside the other day looking down on an unnamed tributary of Rock Creek in north Georgetown. The afternoon was still, cold and December dark, but I was in the company of a few people who seemed to chase the gloom and chill away with the radiance that comes from seeing the world as a garden.

The garden in this case is Dumbarton Oaks Park, a 27-acre slice of wooded stream valley that has suffered through the decades in no small part, perhaps, because of its hidden aspect. It is well known to folks who know it, if you catch my drift, but the park forms an unseen hollow between its elevated and disparate neighbors, which include Dumbarton Oaks, the eastern edge of Wisconsin Avenue and Whitehaven Street.

In the 1920s and 1930s, the masterful landscape architect Beatrix Farrand took this natural area and created a private idyll of meadows, woodlands, paths and 18 decorative ponds, dams and other features as a “wild” counterpoint to her creation of formal terraced gardens above it. In the 1940s, Robert and Mildred Bliss gave the mansion and its more formal gardens to Harvard University, and Dumbarton Oaks as we know it became a center of culture and scholarship. The outlying, designed hinterland passed to the National Park Service, stewards of the greater Rock Creek Park. Over the years, Dumbarton Oaks Park has been used by neighborhood joggers, commuters and dog walkers.

Like a lot of city green spaces, the park suffered from general neglect, the ravages of urban stormwater erosion and siltation, and the smothering effects of unchecked invasive vines and other weeds.

Given the magnitude of its slide and the limits of public and private funding, restoring the park has at times seemed like an impossible dream, but in 2010 a particularly determined group named the Dumbarton Oaks Park Conservancy formed to take up the challenge.

I hadn’t seen the park since, so when conservancy members offered a tour recently I was keen to take a look, even if I was not expecting to see much progress.

My expectations should not have been so low. With the help of some grants and legions of volunteers within and outside the conservancy, the two acres or so around the main entrance to the park (down Lover’s Lane next to Montrose Park) have been transformed.

Even in the emptiness of the season, the progress is evident: Slopes have been cleared of invasive ground covers, stabilized with serious jute anti-erosion matting and planted with native ferns and other woodland plants. Here alone, members of the Georgetown Garden Club planted 2,000 bluebells. In the Bridge Hollow, an area that looks up to and still connects with the cherry trees of Dumbarton Oaks, logs of coconut fiber form erosion control devices while the fresh vegetation takes hold. Lindsey Milstein, president of the conservancy, sets aside a line of wire fence to show me the young native trees now taking hold here, tulip trees, American hornbeams and halesias among them.

Across the stream, in an area known as the Beech Grove, crews removed 70 invasive trees, including Norway maples and ailanthus, dozens of churlish, uninvited shrubs and the usual weedy thugs: English ivy, bittersweet, porcelain berry and Japanese honeysuckle.

This effort was called the Signature Project, designed to demonstrate what can be achieved throughout the park. Although it was substantially completed in the spring, work was still underway in late fall. Milstein led me to the top of the far embankment to meet the conservancy’s Ann Aldrich and Nancy Yoshikawa, who were sowing seeds of at least four species of native grasses. “They will stabilize the slope while the trees we put in grow up,” Aldrich said.

Milstein opened a clear plastic bag full of the seed of a native grass named deer tongue — she had collected it a day or two before from other parts of Rock Creek Park. She handed me some, and we cleared the leaf litter at our feet to expose the soil and proceeded to scatter the seed. “The beauty of this to me is that we gleaned this seed ourselves from this environment,” she said.

Farrand designed a necklace of five small meadows, each separated by a finger of woodland. Earlier this year, the conservancy restored the two meadows closest to Beech Grove, a project that included ripping out the runners of the entrenched vines of wisteria, bittersweet and honeysuckle. Fifty volunteers spent two Saturdays hand-pulling the carpet of Japanese stiltgrass.

Larry Weaner, a Glenside, Pa., meadow expert, designed a seed mix of grasses that included little blue stem, purple top, sideoats grama and blue grama grass. The seeds were sown with a scarifier that minimized soil disturbance, he said. Conventional soil cultivation would have brought up a lot of dormant weed seeds and risked soil erosion. Weeds will continue to sprout, but because the initial planting was only of grasses, the pesky vegetation can be beaten back with spot treatments of herbicide that kill only broadleaf plants. Once they are controlled, wildflower transplants can be added to the meadows, he said.

The Signature Project and the meadow plantings have brought into focus Farrand’s original design intentions, including the relationships between the meadows and the wooded areas. Both had been smothered by the invasive plants. The clearing and replanting has also revealed the romantic character of the terrain.

Nathan Adams, a Park Service spokesman, said the partnership with the conservancy represents “a huge leap forward and we are making good progress.”

But the Park Service and the conservancy still confront massive and costly challenges, including many acres in the southwestern park that are choked with vines, along with the destructive forces of storm water from surrounding properties. Liza Gilbert, the Signature Project’s leader, speaks of “the environmental clouds that are beyond our border. All urban parks are struggling with these very issues.”

Still, the past couple of years have seen real, tangible progress in what is clearly a long slog to restore the park’s health and Farrand’s vision. It’s as if someone had applied polish to a piece of tarnished and dented old silver, and revealed a glimpse of concealed beauty. The impulse is to keep polishing.

More from The Washington Post

Why we need horticulturists

How to care for your Christmas tree

What you need to know to care for holiday greenery

Poinsettias are ready for their close-up