Northern Virginia's 10th and newest regional park, Red Rock Wilderness Overlook on high bluffs overlooking the Potomac River near Leesburg, was officially opened this month by the 86-year-old woman whose donation last summer made the park possible.

The 67-acre park, with river vistas, three miles of woodland trails and a 19th Century farmhouse and barns, becomes the Northern Virginia Regional Park Authority's second park on the upper Potomac and a key part of its long-range goal to protect the Virginia river shoreline from Harper's Ferry to Great Falls. The C&O Canal National Historical Park protects the Maryland shore.

The Park Authority last year completed purchase of 26 miles of Occoquan-Bull Run shoreline to protect the Occoquan Reservoir, the water supply and major park for much of Northern Virginia.

In 1975, the Park Authority created Algonkian Regional Park, on the Potomac near the Loudoun and Fairfax County border, which has almost two miles of river frontage as well as a championship golf course and soon-to-be-completed swimming pool. Red Rock has half a mile of river frontage.

Both parks were bought with matching grants from the Virginia Commission on Outdoor Recreation - $425,500 for Algonkian and $132,500 for Red Rock.

Named after the color of its rocky cliffs, Red Rock was sold to the Park Authority at half its $265,000 appraised value by Frances Valiant Speek, who bought and restored the river farm with her husband more than 30 years ago. She moved to California last year after the place had become "too much for me to keep up."

"I've never cut a ribbon before," she told a small crowd of Loudoun County, state and regional park officials earlier this month at the opening ceremony beside the ruins of fieldstone barn. Later a homemade lunch of fried chicken, beans and coleslaw was served in a restored cow barn where swallows swooped over the tables and occasional butterflies passed through.

"These are the greatest people in the world . . . the finest organization that can be found to carry out a project like this," she said, referring to the authority staff and board members who have preserved more than 8,000 acres of parkland in Northern Virginia since the regional park group was founded 20 years ago.

The opening was timed to coincide with Speek's visit from California and to permit visitors to use the park this summer, although the park trails will not be completed until next year, said Park Authority Executive Director Darrell Winslow. Leesburg Boy Scouts are building woodland bridges for the trails, and split rail fences will be needed to keep visitors from toppling from the 200-foot cliffs.