Growing up in the White Oak area of Silver Spring in the 1950s, James Sorensen listened to his uncle's tales of a mysterious tunnel burrowed between the sides of a horseshoe-shaped bend in nearby Paint Branch creek. He said the tunnel, called Devil's Den, had been blasted through solid rock by a slave--whose owner wanted to build a mill there--in exchange for his freedom.

During the Civil War, according to the stories, it was used to hide horses. Devil's Den also became part of local folklore about the Underground Railroad.

The tunnel has been inaccessible to the public since the Navy bought the property in 1945. For many years, the land was part of the Naval Surface Warfare Center and is now part of the Federal Research Center on New Hampshire Avenue. Many assumed Devil's Den had been blown to pieces as a sewer line was sliced into the banks alongside Paint Branch in the 1960s.

Last November, however, a botanist searching for rare plants stumbled across the tunnel.

"I came to a depression, and I thought this is very, very curious," recalled John Parrish, the Silver Spring botanist who found the tunnel during a trip with the local environmental group Eyes of Paint Branch. "All of a sudden it struck me that this was probably Devil's Den and that I might be the first person to see the place in 50 years."

Obscured by rocky culverts and layers of crumbling leaves, the tunnel, about six feet high at its tallest spot, stretches 35 feet. Several vulture feathers cling to the moss-covered rock at the tunnel's entrance. Inside, the mica walls shimmer.

For Sorensen, now an archaeologist with the National Capital Park and Planning Commission, the discovery validated at least part of the oral history handed down in his family.

Sorensen and about 35 other archaeologists, environmentalists and historians toured the site for the first time in June. It remains closed to the general public.

"To find something like this preserved and to find that folklore has been affirmed is rather interesting," Sorensen said.

But piecing together the tunnel's history and its significance has been filled with contradictions and dead ends.

There is no evidence that a mill was ever built near the tunnel, although other mills dotted Paint Branch and other streams in the mid-1800s. At the same time, the tunnel is constructed like other "mill races" built at the time to channel rushing water from a stream to power a mill. One-inch holes drilled into the stone show that the tunnel was blasted out and was not a natural occurrence, Sorensen said.

The county eventually will do an engineering study to determine whether a mill was built, Sorensen added, and will try to determine who owned the property in the mid-1800s.

One of the earliest written accounts of Devil's Den appeared in The Washington Star in 1914. For 15 years in the early part of the century, J. Harry Shannon trekked across the Washington area, writing about his walks in a column called "With the Rambler."

"It is an uninviting looking place," he wrote. "The Devil's Den at one time was said to be a popular resort for snakes, and it has every appearance now of being able to afford them splendid accommodations."

Nonetheless, Shannon wriggled his way through the tunnel and heard from his unnamed guides the story of the slave who built the tunnel. They told him: "The slave labored with a sledge, drill, gunpowder and fuse for many months. Before the task was done, slavery in Maryland was abolished, but the tunnel cutting man kept at his work till the rock was drilled."

This account, however, contradicts those by Sorensen's relatives, who said Sorensen's great-great-uncle used the tunnel to hide horses from Union and Confederate soldiers who wanted to requisition them for use in the Civil War. It would also mean that the site could not have been part of the Underground Railroad.

Historian Anthony Cohen, who has documented Underground Railroad sites in Montgomery County and written a booklet about his research, and who has also walked an Underground Railroad route from Maryland to Canada, said that it is unclear whether the tunnel had been part of Underground Railroad.

"It makes sense in terms of a great hiding place, a shelter. It's also near a water conveyance, because fleeing slaves traveled along streams by day and highways at night. But that's where we kind of drop off," said Cohen, who heads the Menare Foundation in Silver Spring. The foundation takes its name from a password used by slaves when seeking shelter at a house on the Underground Railroad.

Cohen said that a house on Shaw Avenue, less than two miles from Devil's Den, had been used in the Underground Railroad. In addition, there were early Quaker settlements in the nearby Colesville area, which have been associated with the Underground Railroad. He also said the presence of an African American community, called Stewartown, built after the Civil War and adjacent to what is now the Federal Research Center, makes it likelier there were sympathetic people who might have hidden runaway slaves in the area.

"These were things based on local legend, oral history and speculation that I was able over time to confirm. The same might hold true for Devil's Den someday," Cohen said.

The last known written reference to the tunnel was in an issue of a neighborhood newsletter called the Hillandaler in 1940, which talked of guided walks for children back to the tunnel and a nearby swimming hole.

Gary Irby, who lived next to the Naval Surface Warfare Center for 25 years and now lives in Wheaton, also heard stories about Devil's Den. He and his children combed the nearby woods for the tunnel but never found it.

Then, several years ago, when the family still lived in White Oak, an elderly African American man rang Irby's doorbell. He told Irby that when he was a boy he had played with descendents of the man who built the tunnel.

For Roseanne Price, who wrote about the tunnel for the newsletter Eyes of Paint Branch, making her way through the passageway helped authenticate the stories.

"I really got the sense of what it would take to make this tunnel, how much someone would have wanted his freedom to lay his life on the line to blast through the rock," she said. "Being inside it you think about those who had gone before you."