Rock Creek Park, a new illustrated history of Washington’s signature public park, was conceived by a Washingtonian—while traveling in Massachusetts. It was a couple of years ago: Gail Spilsbury, a Tenleytown resident, was visiting the Frederick Law Olmsted National Historic Site in Brookline. There, she noticed a decades-old volume detailing the early plans for Rock Creek Park—plans drawn up by the famed landscape designer’s namesake son and stepson.

Spilsbury was struck by what she saw. After years of living on and off in Washington, she’d come to love Rock Creek Park’s open spaces and natural look. So she went on to assemble a lavishly illustrated 96-page volume that’s just been published by Johns Hopkins University Press. It’s the first history of the park written for a general audience.

To Spilsbury, Rock Creek Park is worthy of such attention for two reasons. One is size: In D.C. alone, the National Park Service oversees 1,755 acres—more than twice the area of New York’s Central Park. And that doesn’t count the contiguous areas in Maryland, run by the Maryland-National Capital Park and Planning Commission.

The other reason, Spilsbury says, is that most of Rock Creek has remained more or less in its natural state. “Many urban parks have buildings and restaurants and pavilions,” Spilsbury says. “But if you look at Rock Creek Park, you see lots of dead trees that aren’t cleared out. That’s how the forest works.”

Rock Creek Park remains in that state thanks to a large dose of good luck. A number of mills, built generations ago, still stand within the park’s boundaries, but most of the land was never developed—the terrain was too hilly to support agriculture. By the 1860s, visionaries had begun pushing for the creation of urban parks to serve as bulwarks against pollution, overcrowding, and disease. But an initial effort to establish Rock Creek Park stumbled—at first because of the Civil War, then because members of Congress felt reluctant to spend money to spruce up a city few of their constituents would ever visit (and from which the lawmakers themselves typically escaped as soon as a legislative session ended). Technically, the park came into being in 1890, but it began to mature into its present state only after a 1918 report written by Olmsted Jr. and his brother Charles.

In addition to providing recreational assets to the city, Rock Creek Park shaped Washington’s future development patterns, Spilsbury says. “After the Civil War, the population in D.C. went way up,” she says. “Once you had the park, this growth could never go through the park—it had to go around it. Today, on the park’s fringes, you can see rich people’s homes. That’s the kind of development that would have happened everywhere else if it hadn’t become a park.”

Spilsbury, 50, has nurtured an appreciation for landscape ever since growing up on a 5-acre wooded-and-landscaped lot in Milton, Mass. She later spent years as a freelance writer and foreign-service spouse in Italy, Guyana, and Poland; today, she’s a senior editor at the Smithsonian’s Freer and Sackler Galleries (and, in her spare time, a screenwriter).

Her volume on Rock Creek Park led to her next book, due out later this year. It collects sketches of Washington-area sights made during World War I by Robert Dickinson, a physician who happened to be stationed here. Before Spilsbury located Dickinson’s drawings at the Library of Congress, she says, his works “had not seen the light of day in decades.”

“And they’re beautiful. When I located his family, they were so happy—they didn’t know these drawings existed, either.” —Louis Jacobson