Jeanne Minor gives a demonstration at Peirce Mill in Northwest Washington. The mill is one of four in operating condition in the metro area. (Nathaniel Koch/Nathaniel Koch)

Sitting in Rock Creek Park at Tilden Street NW and Beach Drive is a living relic of Washington history: Peirce Mill belongs to the era when the nation's capital was also an industrial town.

Now a National Park Service site and on the National Register of Historic Places, the mill is accessible from the Rock Creek bike trail and can make for an exceptional break during a ride. In addition to the mill, there's a carriage barn and an orchard. Completed in 1829, this small grist (flour) mill is one of more than two dozen mills (eight in the District) that ran on Rock Creek water; even larger mills stood along the Potomac in Georgetown. It's the only D.C. mill still in operating condition and one of only four such mills in the Washington region.

In the 1780s, a Quaker entrepreneur named Isaac Peirce moved from Philadelphia to Washington. Within a few years, his family owned almost all the land that is now Rock Creek Park. The mill was one small part of what became a large family-run agribusiness. It was supported by slave labor. The mill ground corn, wheat and rye, according to the Park Service.

By the 1840s, milling had become Washington's No. 1 industry. But 50 years later, with Mid-Atlantic milling in decline and nationwide historic-preservation and parks movements underway, the United States bought the Peirce land. Since then the mill has been restored several times, most recently (since 2001) by the Friends of Peirce Mill, a nonprofit group and Park Service partner.

Inside the rough stone millhouse is what was once a state-of-the-art automated factory. Older mills had half a dozen workers doing heavy labor — but this kind of mill, patented by Philadelphian Oliver Evans, essentially ran by itself, with supervision from an operator or two.

"It's almost 200 years old and it still works," says Jeanne Minor, Peirce's first female miller. Minor is in period costume on the second and fourth Saturdays of the month for demonstrations. Female millers, Minor adds, were so rare that she had to improvise her costume.

The site hosts more than 10,000 visitors a year. (Last year, the Park Service says, there were more than 13,000.) From April through October, the mill is open Wednesday through Sunday. Friends of Peirce Mill also holds events, including a Heritage Day on Oct. 14. (For more info: friendsofpeircemill.org.)