Under a bright sun that made the Potomac River and its snowy banks look as if they were sprinkled with diamonds, federal and local officials yesterday dedicated a hiking trail winding 2.5 miles between Riverbend Park and neighboring Great Falls Park.

Speakers recalled the words of poets, presidents and naturalists as they stood under a green-striped awning at the Riverbend Park end of the newly christened Potomac Gorge Interpretive Trail. Geese could be heard honking, ducks paddled past in the river and tree branches bowed low under the weight of snow.

"In parts of the county, it's hard to believe you're in a big, urban county with more than a million people," said Fairfax County Board of Supervisors Chairman Gerald E. Connolly (D). "Trails open up nature for our fellow citizens, some of whom only know the urban parts."

Park officials hope the riverside trail will introduce more people to the river and its cultural and geological history.

The trail, a well-tended dirt footpath, is not new. It has been there for many decades, beaten down by untold numbers of hikers. In the 19th century, residents of Washington rode a railway to the park, which had campgrounds, a carousel and an inn.

Now, with $20,000 in federal funds, matched by $20,000 from Fairfax, officials at the national Great Falls Park and the county Riverbend Park have installed 14 signs along the shoreline trail. The signs explain various aspects of the gorge -- its formation during the ice age, the wildlife and plants and the way humans have altered the river, lived off it and entertained themselves along its banks.

Some of the signs are written with wry amusement.

"How'd This Sand Get Here?" is the title of Signpost 2, outlining 200 million years of erosion from the Blue Ridge Mountains 35 miles away.

"Creatures of the Seep" at Signpost 7 lists some of the critters that live in the soil and dead leaves, like the mud salamander, dragonfly and a tiny quarter-inch animal called a scud that looks like a bean sprout.

"Why Is There a Hole in That Rock?" on Signpost 12 explains how floods 35,000 years ago carved large potholes in the rock over a 500-year period.

Several speakers said it was important to maintain a large park amid all the development in the region. The roads leading to the two parks are lined with new, sprawling "estate" homes that have been built recently or are in developments still under construction.

"We're increasingly challenged by open space needs as the population grows," said Kevin J. Fay, a member of the Fairfax County Park Authority Board.

Fay said that in a recent survey by the Park Authority, residents cited hiking trails and open space as the most desirable amenities they seek more of, above athletic fields.

Among those attending the dedication ceremony were several McLean High School seniors who are in an Advanced Placement environmental class and had volunteered to help set up the chairs.

"It's pretty amazing that it used to be the seafloor and it came down to form a gorge," said Nathaniel Wallshein, 17.

"Yeah, it originally was as high as the Alps," said Bret VandenBos, 18.

A classmate was as amazed at the present as the distant past. Jordan Bridges, 17, recently moved to the area after his family's New Orleans home was destroyed by Hurricane Katrina.

"I've never had a bagel or a gingerbread cookie," he said as he munched on a bagel smeared with cream cheese. "I've never seen snow or winter or anything like this. I feel like a kid. I want to jump in the snow."

Federal and local officials gather around the first of 14 interpretive signs along the Potomac Gorge Interpretive Trail in Great Falls.Signpost 5, "Travelers From the Tropics," lays out for visitors which songbirds and hawks from warmer climates are drawn to the river gorge each spring.