Bash Bish Falls is located in Massachusetts, just over the border from New York, but one of the trails that leads to it, the Bash Bish Falls Trail, begins in Taconic State Park near the town of Copake Falls, N.Y.

Because Dunn wants his books to serve as historical texts as much as guides to pretty picnic spots, he includes extensive references in the back. The ''Hudson Valley Waterfall Guide,'' for instance, has more than 70 pages devoted to footnotes, bibliography, and index.

Dunn and Delaney are often called upon by community groups to lead ''history hikes'' to destinations that are rich in cultural as well as natural history. Waterfalls are often steeped in history, since they provide energy for industry as well as inspiration for poets and painters.

''One of the things that appeals to me in working on the books is the sense of adventure in searching for these natural treasures,'' said Dunn, who divides his time between a home in Albany and a camp on the Great Sacandaga Lake, 40 miles to the northwest in the Adirondack foothills.

''I've always collected old postcards, and it's fun to have one of a waterfall that was very popular in Victorian times and try to find it again,'' Dunn said. ''It's exciting to find a beautiful place people have lost track of over the years. Of course, we've also been to many desolate gorges and ravines looking for waterfalls, only to come up with nothing.''

Dunn includes old postcard pictures of waterfalls as illustrations in his books.

The popularity of waterfalls is evident in the large number of Web sites devoted to them on the Internet. One site, the World Waterfall Database, seeks to catalog the world's most significant waterfalls and rate them according to size, beauty and other factors.

''I'm not certain just what quality a waterfall possesses that intrigues me so,'' writes Dean Goss of Jericho, Vt., co-creator of the World Waterfall Database. ''Maybe I like the sound, maybe I like the geometry, perhaps I am awed by the power water has over rock, perhaps the negatively charged ions that remove impurities from the air has something to do with it.''

The sound of a waterfall has much to do with its appeal, Dunn said. Like the wind howling through hemlocks or waves pounding on the shore, ''waterfalls are the voice of nature, powerful and majestic, beckoning and mesmerizing,'' he writes in ''Hudson Valley Waterfall Guide.''

And they offer an ever-changing show over the seasons: splashing into pools reflecting brilliant foliage in the fall, freezing into dramatic blue pillars in winter, surging with fury in the spring, and trickling languidly over mossy ledges in midsummer.

''I think people today have the same reaction to waterfalls as the Victorians did,'' Dunn said. ''We're fascinated by the sublime and the awesome, mesmerized by these entities of rock and water.''

____

If You Go...

WATERFALL GUIDES: Russell Dunn's ''Mohawk Region Waterfall Guide'' ($15.95), ''Hudson Valley Waterfall Guide'' ($17.95), ''Catskill Region Waterfall Guide'' ($14.95) and ''Adirondack Waterfall Guide'' ($14.95) published by Black Dome Press, http://www.blackdomepress.com/ or 800-513-9013.

WATERFALLS: Here are some scenic spots described in Russell Dunn's waterfall guides:

-Bash Bish Falls: Near Copake Falls, 40 miles south of Albany at the Massachusetts state line, reachable by an easy, half-mile walk on a gravel road through forest bordering a boulder-strewn stream with numerous pools and picnic spots. The spectacular, 80-foot-tall waterfall drops from high cliffs into a clear, bowl-shaped pool that's a popular swimming hole in hot weather. Described in ''Hudson Valley Waterfall Guide.''

-Cohoes Falls: A registered National Historic Landmark 10 miles north of Albany near the confluence of the Mohawk and Hudson Rivers, reachable by a roadside overlook. The 70-foot-high, 600-foot-wide falls once rivaled Niagara as New York's premier natural wonder and was visited by thousands of tourists each year. Today, its shaly ledges are mostly dry much of the year, as the water has been diverted for hydroelectric generation and the Barge Canal. Described in ''Mohawk Region Waterfall Guide.''

-Roaring Brook Falls: Along Route 73 in Keene Valley in the Adirondack High Peaks region, 100 miles north of Albany. This narrow flume plummets from the shoulders of Giant Mountain. A jumble of huge boulders at its base is a popular climber's playground, and rock jocks are often seen scaling precipitous cliffs above. It's also popular with ice climbers in winter. Described in ''Adirondack Waterfall Guide.''

-Kaaterskill Falls: A half-mile hike from Route 23A in the Catskill Mountains near Palenville, 36 miles southwest of Albany. The 300-foot, two-drop waterfall was an icon subject for Hudson River School painters Thomas Cole and Asher Durand, as well as an inspiration for influential naturalists, authors and poets of the 19th century. The trail to the falls is steep and treacherous, but is the most-hiked trail in the Catskill park. Described in ''Catskill Region Waterfall Guide.''

WORLD WATERFALL DATABASE: http://www.world-waterfalls.com/