On May 31, 1889, high in the mountains above Johnstown, Pa., the South Fork Dam collapsed suddenly and let loose 20 million tons of water. The deluge rushed down the narrow gorge of the Conemaugh River Lake, which was already swollen by the same heavy rains that destroyed the dam. Forty-five minutes and 14 miles later, a massive wave crashed down on 30,000 unsuspecting townspeople with a fury seldom matched in human history.

Even now, the stories -- told in museum displays and local lore -- echo through the valley. Like this one: Minutes before the flood waters reached Johnstown, 16-year-old Victor Heiser went to the barn behind his family's store to tend to the horses. Hearing a terrifying roar, Victor climbed onto the roof of the barn. He braced himself as a 30-foot wave demolished the store and ripped the roof off the barn. Victor clutched the roof helplessly for 10 minutes as it surfed across the wrecked city until he came to a rest more than a mile from where his home had stood.

When the waters receded, four square miles in the heart of the steel and coal boom town between Pittsburgh and Harrisburg were devastated, 2,209 lives were lost, and many thousands more were homeless. Victor lost both his parents.

At the time, the Johnstown Flood generated unparalleled interest. Hundreds of reporters descended on Johnstown, and assistance came from as far away as China. Washington's own Clara Barton spent four months in Johnstown administering aid in the American Red Cross's first major relief effort.

I went to Johnstown in search of the history and legend of this epic disaster, and began at the Johnstown National Flood Memorial at the dam site in present-day Saint Michael. The remains of South Fork Dam still peer down on South Fork Creek as the now quiet stream wends between oaks and poplars. As I stood atop the dam abutments 70 feet above and looked back at the empty lakebed, the topography that made the flood possible was obvious.

The valley is a great bowl and I could easily envision the 21/2-mile-long reservoir that served as an exclusive summer retreat for some of the Industrial Age's wealthiest scions, including Andrew Carnegie and Andrew Mellon. Sailboats and two small steamships plied the lake's waters. Several lakeside "cottages" -- actually lavish Victorian mansions -- are still visible on the far side of the valley in various states of dilapidation. They are stranded high above the lakebed, now a meadow flush with fading fall colors.

When constructed in the 1850s, the earthen dam was the largest of its type in the world -- more than 70 feet high and 900 feet across. A debate still rages as to whether its collapse resulted from the neglect of basic maintenance by the South Fork Fishing and Hunting Club or whether it should be attributed solely to the eight inches of rain dropped by a storm. Contemporary lawsuits vindicated the club's wealthy members, but public opinion condemned them. On the 100th anniversary of the catastrophe, an article in Civil Engineering magazine concluded, "If South Fork Dam had been rebuilt to the original specifications and construction, the disaster of May 31, 1889, never would have happened."

The National Park Service visitor center was designed to resemble a 19th-century barn and sits next to the restored caretaker's house. Panels explain how the caretaker worked frantically, and in vain, to reinforce the dam as it eroded under pressure of the swollen reservoir.

Inside, an interactive diorama illustrates the day's events. The narration weaves the stories of individual victims and survivors, including a taped oral history by Victor Heiser, who was the last known survivor when he died in 1972. As Victor tells his story, a multimedia collage vividly depicts the tangle of debris carried by the wave.

The visitor center also shows "Black Friday," a 35-minute film in ethereal black-and-white. Its graphic reenactment of the flood had me gripping the armrests of my seat.

The collapse of the dam let loose a wave carrying the force of Niagara Falls many times over. It sped down South Fork Creek and then the Little Conemaugh River, reaching speeds of 40 miles an hour and towering 76 feet high where the valley narrowed. It bulldozed everything in its path, sweeping away houses, toppling stone bridges and carrying off 40-ton locomotives "like corks."

The only warning given Johnstown was a great black mist and ominous rumbling. When the flood crashed through, the surge was more than 30 feet high. The wave wiped out entire city blocks. A 45-acre pile of debris collected at a seven-arch stone bridge, which still stands. Hundreds of people were caught in the mass, which was soaked in oil and tangled in barbed wire. Fires burned for three days as rescue workers tried to free victims, some trapped in their dislocated houses.

Today Johnstown is a 20-minute drive from the dam site. The locally run Johnstown Flood Museum is housed in a stunning French Gothic library building funded by Carnegie to atone for the devastation wrought upon the city. There is an extensive collection of artifacts and explanatory panels that focus on the human toll of the flood and the public's triumph in its aftermath. The museum also has an Oscar-winning film by Charles Guggenheim. Its more academic and informative approach provides a nice contrast to the gritty, emotional film at the Park Service memorial.

At the museum, an 18-page, $1 pamphlet outlines a self-guided walking tour of the city. The 16 stops include surviving structures and post-flood construction, each explained with anecdotes and after-the-flood pictures. At the First Methodist Episcopal Church, I touched the cool pink sandstone that stood fast against the direct impact as water crashed through windows and reached a height of 18 feet in the sanctuary. Nearby Alma Hall was spared the brunt because it stood in the shelter of the church. Among the 264 victims who found refuge on the upper floors was William Matthews, a physician who suffered three cracked ribs. He attended to two babies born during the night.

The destroyed City Hall was replaced in 1900 with a handsome example of the Richardsonian Romanesque style that dominated American municipal architecture at the time. A plaque on the side of the rebuilt hall shows the high-water level for another major flood in 1936. Twenty-five people were killed. Standing on my toes, I could barely reach the mark of 8 feet 6 inches.

Eventually, the river was deepened and channelized behind concrete walls and Johnstown was pronounced "flood-free." But another massive storm in 1977 caused the river to rage once more, causing 85 deaths and $200 million in property damage. It seems Johnstown's topography simply can't be subdued and the city now proudly, if fatalistically, proclaims itself "Flood City."

The 1889 Johnstown Flood in Pennsylvania killed more than 2,000 people. Clara Barton came with the American Red Cross's first major relief effort. The people standing on the rooftops above were probably sightseers. A Carnegie library, built just after the flood, now houses the Johnstown Flood Museum.