For all its seemingly pristine beauty, Rock Creek Park has worn many faces over the years. Before it became synonymous with touring bikes, Frisbees and jogging, it was a setting for 19th century gristmills, orchard farms and logging. Before that, its steep, craggy slopes were the site of Native American quartzite mines.

Then in 1890, the 51st Congress and President Benjamin Harrison declared 1,750 acres of it a federal park, preserving its rustic beauty for generations.

To celebrate the 100th anniversary of that decision, the National Park Service is planning some special events this year, and the kickoff is a rich show of 36 historical photographs of the park and people in it dating back to the Civil War.

The photographs, fittingly, are displayed in the entrance hall of the rustic Art Barn, the park gallery housed in a carriage house circa 1800 that was built of blue granite quarried at nearby Broad Branch creek.

A walk through the exhibit is much like turning the pages of a musty old family album of familiar scenes with a flavor of the past, many without names or dates, their identities long since lost to time.

For all we know, the men and women in their turn-of-the-century Sunday best perched atop rocks by the rushing creek in one photograph may be the great-grandparents of some of today's parkgoers.

There have been exotic gatherings, such as the one recorded in a 1890 photograph of the processions of elephants that used to make their way down the hill behind the National Zoo twice a day to bathe in the tree-lined creek.

A few photographs date to before the park's formation, when, during the Civil War, the hills overlooking Rock Creek were incorporated into the ring of forts that defended Washington.

Today the park encompasses 2,800 acres, making it one of the largest urban parks in the world, as well as one of the most dramatically pristine city spaces.

The expansive creekside park extends between the Maryland line and the Potomac River, creating a fairly intimidating gorge for traffic to cross.

In the early years, the solution was a system of fords, captured in one photograph as one of the park's early rush hours: A half-dozen 1920s automobiles after a heavy rain are trying to cross a ford near present-day Beach Drive and Broad Branch Road.

The past century has seen all but one of the fords replaced by bridges, including some of the area's most handsome spans. The change is documented in a 1930s shot showing construction of the P Street Bridge beside a spindly trolley bridge with the graceful arches of the Buffalo Bridge at Q Street rising in the background.

In contrast, Boulder Bridge, sheathed in large fieldstones, was built to blend with its setting and appears like an apparition curving up through surrounding undergrowth.

This was the bridge made famous shortly after its construction in 1902 when President Roosevelt advertised a reward for a gold ring he had lost in its vicinity.

Still a favorite of parkgoers, Boulder Bridge appears many times in a show of local art that accompanies the exhibit of photographs. Organized by the Art Barn Association of local artists to celebrate the park's centennial, this show, although uneven, demonstrates how Washington's artists continue to respond to the park's natural beauty.

Capturing the park's changing seasons and often startling effects of weather, several of the pieces, with timely concern, also focus on environmental issues.

It was conservation, after all, that prompted the founding of Rock Creek Park, just four days before Yosemite National Park was chartered. In a quote accompanying the old photographs, President Woodrow Wilson, who courted his second wife on walks in the park, calls it " . . . the most beautiful thing in the U.S. . . . to mar its natural beauty . . . would be to do an irretrievable thing."

Several photographs seem to echo this thought: a dogwood branch fanning out over the water, a quiet stretch of creek flowing past a set of abandoned wagon wheels, a bridge blanketed in snow -- timeless images still available for view today because of a 100-year commitment to park preservation.

The show continues through Sept. 2 at the Art Barn, at 2401 Tilden St. NW, open from 10 a.m. to 4:30 p.m. Wednesday through Sunday.