The day after Hurricane David hit Washington, Rock Creek park ranger Mac Palmer went out to inspect the damage and was amazed to find the usual hikers, bikers and joggers making their rounds through the debris.

Two of the bike-trail bridges were completely washed out, but the people were back, Palmer said, "just jogging and biking all over the place. And I think the bulk of them were out there to use the park, not to see the damage. It was like then were saying 'By golly, no storm's gonna stop me.'

"It's amazing to realize how much this place is used, and how much it means to people."

As the capital's playground, Rock Creek heads into its 90th year this month, and a big bash Saturday makes it all official. "Rock Creek Park Day" activities are scheduled from 1 to 5 in and around Peirce Mill, in the park at Beach Drive and Tilden Street NW. (Rain date is Sunday). More than 25 embassies will sponsor art exhibits, song and dance, and an international bazaar. A hot-air balloon will ascend, a steel band will play and park employees will lead nature hikes, rides and games. At the center of it all will be Peirce Mill, where millers grinding grain and selling it will recreate the sights and sounds of the 19th century.

The party-goers will have to compete with Rock Creek Park's regulars-the more than 10,000 people who drive, hike, canter, bike, skate, picnic and jog their way through the park each weekend.

On a crisp fall afternoon, as many as 200 people may flock to one of the nature center's weekend hikes, in search of small wonders. Rock Creek's mile-wide, four-mile-long course-twice the size of New York's Central Park-is home to more than 30 species of mammals, 145 different kinds of birds, nearly 50 amphibians and reptiles and 33 fish species, not to mention hundreds of different trees and wildflowers. The 1,800 acres are packed with miles of trails, for biking, hiking or horse-riding. There are stables, picnic groves, a nature center, planetarium, amphitheater and golf course, and courts for tennis, football, baseball, softball, volleyball, horseshoes and archery.

A little more than a hundred years ago, when Rock Creek Park was just a gleam in Congress' eye, naturalist John Burroughs saw the potential in the heavily-wooded creek valley. "There is perhaps not another city in the Union that has on its very threshhold so much natural beauty and grandeur, such as men seek for in remote forests and mountains," he wrote in 1863. "A few touches of art would convert this whole region into a park unequalled in the world." Thirty years later, on September 27, 1890, President Benjamin Harrison dedicated the park as "a pleasure ground for the benefit and enjoyment of all people of the United States."

Nearly a century later, Rock Creek Park is still a "pleasure ground." On a weekend afternoon, a steady stream of joggers pound the paths as would-be artists prowl with their sketch pads. Some of the artists take free lessons at the Art Barn. At a recent gathering a dozen students-white-haired matrons, teenage girls-sketched pastoral scenes.

Dressed in a flowered sundress and sandals, a woman sprawled in the shade in front of Peirce Mill and made tentative scratches on a sketch pad. It was the first time she'd visited the park, she said, and it was only because her daughter had dragged her along. "But I'll definitely come back. You can't ask for more," she said. She looked doubtfully from the paddlewheel to her sketch and drew another line.

Down in the mill's cool, damp basement, George Sumner, a sculptor from the District, sketched a more intricate scene-the gears and wheels that power the mill. "Everybody else is doing those pictorial scenes, but I'm fascinated by these shapes," he said. He had two hours to complete his drawing and take it back to his teacher for criticism.

As Sumner sketched, parents and their children tramped up and down the stairs. The resident miller, an overall-clad, strawhatted Park Service employee, patiently answered their questions. "Sometimes I think I'm a tape recorder," he sighed, and stepped out the side door for a quick smoke.

Outside, the lines of cars turning into the parking lots were growing longer. A parade of people, laden with baskets, volleyballs and blankets, headed for picnic tables.

At one table on the banks of the creek, several students and faculty members of the University of the District of Columbia physics department sat around discussing "jobs, classes and the future" while they waited for their classmates to show up. "This is supposed to be our annual picnic," said faculty adviser Marilyn Krupsaw forlornly. "We should've had 20 here at least." Everybody wore a pastel-colored physics club T-shirt labeled "And God said," followed by a mysterious equation which club members said was the formula for the origin of light. Or something.

Krupsaw, an animated woman whose enthusiasm for U.D.C. is equaled only by her enthusiasm for physics, talked up the school's program while Carlos Simmons, 32, a U.D.C. student and faculty assistant, and Charles Small, 19, president of the physics club, moved the picnic table away from a herd of "killer bees." "Physics is the most logical and basic of the sciences," Krupsaw said, and as for her students, "they're not all eggheads. One of the most beautiful girls I've ever seen will be here soon." A few minutes later, a beautiful girl did indeed appear, carrying a badminton racket. The Annual U.D.C. Physics Department Fall Picnic was officially underway.

A few hundred yards down the creek, Joy Duva, 31, a consultant from the District, chased her dog Jango in and out of the stream. "I don't know why it's so brown, but it's not very inviting," she said, and settled down with a paperback in her beach chair while Jango panted beneath a tree.

Just a few yards downstream, a teen-aged couple, both dressed in blue jeans and oblivious to everything around them, were passionately entwined on the creek bank.

At the Rock Creek Horse Center, just a short drive away from the mill area, there's an entirely different ambience. Five women in velvet hardhats rode around the ring clapping their heels over their horses' heads while owner Bob Douglas called instructions from the center of the ring. "Ok. Post and trot," he called out in a weary tone. He teaches all levels, from handicapped children to advanced adults, seven days a week. "A little exercise, please. I'm selling a little walking but nothing else." His voice rose. "I don't see any stretching," he told Wendy Gavel, a photographer from Mount Pleasant. "If you get your thighs stretched maybe your shoulders'll go back."

"I watched him last week and he was just as exasperated," grinned Tom Drummond, a clinical psychologist from the District who was waiting with his daughter, Caroline, 12 1/2, for a trail ride to begin. Drummond, dressed in worn jodhpurs and carrying a riding crop, definitely had the edge over the rest of the dozen or so potential trail-riders lined up along the ring fence. "I may fall off," one of them said nervously to a friend, who didn't look as if she'd be much help.

Elizabeth Velez, an English teacher who said she was the most non-athletic human being in the world, got an "OK" from Douglas as she galloped up to the gate. "He's a good, good teacher," she said, and horseback riding is "the most wonderful thing on earth. It gets your head straighter than a shrink, and it's much less expensive."

Up came another class, already sweating heavily in the afternoon heat. "I got a $40 ticket for speeding over here," a middle-aged woman groused. "The snow could be knee-high and they'd still be out there," Douglas told a visitor. "That's because they love riding," he added unnecessarily.

The sports, or lack thereof, may vary, but the people who come to Rock Creek Park all have the same reason for coming. "It's just relaxing, that's all," said one man who seemed incredulous the question was even asked. "It's nice to get away from the city-the noise, the traffic. . ."

His thoughts were echoed by a transplanted New Yorker, waiting for the "barn brats" at the Horse Center to saddle him a horse. Rock Creek Park is "far superior" to Central Park, he said, and not just because it's safer.

"In Central Park you always know you're in New York," he said. "Here, you forget you're in the city."