Rock Creek and Connecticut Avenue

Preservation of the Rock Creek valley as an extensive and varied public park, where the natural landscape was to be used for recreation, sports, and the simple enjoyment of nature, had its genesis in plans of the 1860s to find a healthier location for the president's house. Proposals in 1867 by army engineer Nathaniel Michler for sites on the high ground in present-day northwest Washington were based upon Frederick Law Olmsted's principles of retaining a site's natural features and enhancing them with public amenities, ideas instituted in New York's Central Park just a decade earlier. In the late 1880s, Washington banker Charles C. Glover, whose grandfather had known L'Enfant, led local business leaders in promoting Rock Creek Park in Congress, as general public health issues, particularly the creek's increasingly polluted waters, were of great concern. The 1890 congressional legislation that established the park for the “benefit and enjoyment of the people of the United States” promoted its national rather than local importance in order to ensure public funding. Washington as a national resource was also envisioned as a model of American civic beauty, a city of gardens, where the country's much-vaunted natural resources would be preserved for all citizens.

Army engineers who were members of the Rock Creek Park Commission, led by Gen. Thomas Lincoln Casey, established the park's boundaries by 1891, while its civilian members, led by Samuel P. Langley, secretary of the Smithsonian Institution, oversaw purchase of the privately held land, a process that lasted until the end of the decade. The park's boundaries were predicated on its topography, a narrow creek bed in its lower third, and broad, rolling meadows and woods where the valley widened above the rugged terrain of the National Zoological Park, about 175 acres, set aside by Congress in 1889, in the ravine that divided northwest suburbs developed in the 1860s and 1870s just outside the city's original boundaries. Frederick Law Olmsted, Jr., the landscape architect for the 1902 McMillan Commission, whose main objective was the revitalization of monumental Washington, was a vociferous supporter into the 1910s of preserving Rock Creek's scenic beauty in its natural state.

The parkway road system, where pleasure driving was included as one of the recreational benefits of the park, was designed in the 1920s and 1930s by the National Capital Planning Commission. Automobile access at limited east-west intersections and a winding and varied roadway that ran from the park's mouth at the Potomac through the Maryland extension of Rock Creek Park, Sligo Creek Park, made the park available to a much larger population than just inhabitants of its contiguous suburban neighborhoods.

In 1892 Frederick Law Olmsted was consulted about the layout of the National Zoological Park ( NW01). As it had been founded to shelter all species of North American animals at the very time when the frontier was closing, the emphasis was on providing natural habitats for the animals insomuch as possible. Thus, in addition to conventional animal houses, extensive pastures for grazing were planned along with natural rock quarries to contain bears, a scheme that was unsuccessful. Two of the original buildings survive, the Principal Animal House ( NW01.1), now the lion house, designed by William R. Emerson of Boston in 1892, and the New Mammal House ( NW01.2), at present the monkey house, completed in 1906 from a design by Washington architects Hornblower and Marshall.

Linnean Hill ( NW02), or the Pierce-Klingle House, located in the park at 3545 Williamsburg Lane NW, was built by nurseryman and mill owner Isaac Pierce (see NW03) in 1823 and named in honor of the Swedish botanist Carolus Linnaeus. Pierce's house is constructed of gray granite fieldstone and follows the common American Georgian vernacular form for an end-chimney type of five bays and two stories. A single-bay, two-story gabled wing replacing the front door was added at an unknown date before 1859. The single-story west wing is an 1843 addition. The house's glory is its south facade, with an elaborate two-story cast-iron veranda (c. 1855) and the remnants of Pierce's gardens framed by two cubic outbuildings set into the slope of a lower terrace. Between 1856 and 1859 Pierce designed and constructed an extensive picturesque garden on his 82-acre estate. Linnean Hill, currently undergoing restoration, was first restored by the National Park Service in 1935–1936.

Rock Creek waters had turned numerous mill wheels even before the city's founding. Pierce Mill ( NW03), restored by the National Park Service in 1934–1936 and again in 1984–1985, is a rectangular, two-and-a-half-story, gable-roofed structure built of uncoursed blue-gray granite and brown-stone quarried locally. The “BIP 1829” inscribed in the south stone gable may refer to “Betsy and Isaac Pierce” or “Built by Isaac Pierce” and the date of the mill's completion. It was probably begun in 1820; the wooden north gable attests to an earlier construction date. Adjacent buildings—the springhouse on Tilden Street, a private house that originally had been a distillery, and a nearby stone barn—were also once part of the plantation, whose extent was comparable to the size of the park today, about 2,000 acres.

Two surviving twentieth-century bridges across Rock Creek typify the dichotomous romantic and pragmatic concerns surrounding the park's genesis. Boulder Bridge ( NW04), which carries Beach Drive over the creek, was designed in 1902 by W. J. Douglas as a single-span arch whose steel-reinforced concrete structure was faced with large stones to achieve a rustic and natural appearance. In contrast, the Ross Drive Bridge ( NW05) of 1907, with its unornamented exposed open-spandrel concrete arch, expressed a functionalist engineering aesthetic much admired for its directness and simplicity.