The first Washington Monument isn't the one on the Mall, and it isn't the one in Baltimore, either, never mind what the plaque says. It's a rugged stone tower hidden away on a crag of Maryland's South Mountain.

Although it's in Washington Monument State Park, whose official pamphlet asserts the tower's primacy, few have heard of it and fewer yet have seen it. The only way to reach the unique memorial is to follow a remote footpath off the Appalachian Trail.

The 34-foot obelisk overlooks Boonsboro, whose early inhabitants built it. At 7 a.m. on July 4, 1827, they ceremoniously set off on a two-mile march up the mountain to the lofty site they had chosen. By the end of the day the mortarless "blue rock" shaft stood 15 feet high on a base 54 feet in diameter. They dedicated it then, finished it that fall, and for years the monument was a popular meeting place.

By 1882, however, weather and vandalism had reduced the tower to rubble; the Odd Fellows Lodge of Boonsboro restored it and Gov. William T. Hamilton rededicated it. An access road was built. But a few years later the shaft collapsed again.

In 1934 the site became a Maryland state park, and the memorial was rebuilt by the Civilian Conservation Corps. The original cornerstone was set in place, with a facsimile of the dedication tablet:

Erected in Memory of Washington

July 4, 1827 by the citizens

of Boonsboro The shady and peaceful park is an ideal place to relax and enjoy an unhurried day. It'll be more exciting than usual this Fourth of July, with a picnic supper in the evening and fireworks at dusk.

In the visitor center are collections of firearms, Indian relics and Civil War mementos. You're invited to picnic, hike, birdwatch and camp. Nearby historic areas include Antietam, Harpers Ferry and Winchester. FIRST WASHINGTON MONUMENT -- For information write Park Superintendent, Washington Monument State Park, Route 1, Box 147, Middletown, Maryland 21769, or call 301/432-8065. To get there: From the Beltway, take I-270 past Frederick to the Braddock Heights exit, go left on Alternate U.S. 40 west and follow the signs.