HOLLENBACK TWP. - Ron Hall led hikers down a gorge and spent two hours pointing out ruins of a gunpowder mill along the Big Wapwallopen Creek before he paused and asked the men in his group to remove their hats.

"I can still feel the presence," said Hall, standing where his great-grandfather, John Rossman, and three other men died in a massive explosion.

The blast occurred on Feb. 10, the coldest day of 1888, at a building called the packing house where workers filled kegs with gunpowder.

Because the temperature was 6 degrees below zero and the snow thigh deep, the horse-drawn rail cars hadn't carted away kegs for three days. Up to 20 tons of black powder piled up that day, a charge equivalent to 40 of the largest conventional bombs in the current arsenal of the U.S. Air Force, said Hall, a retired Army colonel.

The force of the blast startled people for 20 miles in all directions.

"In many places bric-a-brac and flour (sic) pots were displaced," the Hazleton Standard reported the next day. "The buildings shook as if an earthquake had taken place."

Sixty shards of glass critically injured one woman in her home miles from the mill. She survived.

Rossman's hand with his wedding ring was flung a half-mile, practically to his home in the village of Powder Glen where his wife had just returned after walking with him to work.

"He was vaporized," Hall said.

As Rossman disappeared in a flash, he also vanished from the family tree. His widow remarried and took a different name.

Even though Hall had swum in the Wapwallopen as a teenager in the 1950s, he didn't know then what the ruins along shore represented to history or his family.

Later a cousin noticed a strange name on the birth certificate of their grandmother, launching Hall and two other cousins, Richard Martin and Lori Bates, on a search to learn the about the past of their family and the powder mill.

They went to Brandywine, Del., where E.I. du Pont de Nemours and Co. operated a powder mill before buying the Wapwallopen Black Powder Mill. At Brandywine, they watched some of the vintage powder-making machinery operate at the Hagley Museum. In the museum's archives, they examined photographs and documents about the Wapwallopen mill.

Hall, who lives in Midlothian, Va., also went to the American History Museum of the Smithsonian Institute in Washington, D.C., to see turbines like those that powered the powder mill.

He and his cousins, who live near Wilkes-Barre, returned to Wapwallopen, too, where they mapped the mill's layout and took photographs after obtaining permission from the landowner.

Hall compiled what he learned into a 60-page, spiral-bound book. He handed out copies to members of the Pennsylvania Anthracite Section of the Society of Mining Engineers before leading them on a tour of the powder mill.

The tour took place on Earth Day, April 22, and began atop the gorge where the engineers could look down through the trees toward the creek and ponder the audacity of William Silver.

Silver patented a gunpowder-making machine in 1855 and chose to build the mill along the Wapwallopen Creek in Hollenback Township despite the terrain.

Sandstone and siltstone erupt through the sides of the gorge that pitches down nearly 300 feet in places. Atop the gorge, the half-mile trail where workers installed a pipeline 150 years ago now thins to the width of a few boots in places. About half the group decided not to chance it. Those who finished the walk were rewarded by the sight of a mated pair of mallards flying over a waterfall.

Jon Inners knew the way, having walked the pipeline path before while helping map the state for the Pennsylvania Geological Survey. Powder mill workers of yesteryear who excavated a route for the flume - a pipe 36 inches across and a half-mile long - uncovered a contact point between two types of rock in the gorge.

"If it wasn't for the flume, you'd have never seen it," Inners said while pointing to a 10-foot strip of red shale. Below the red strip, the gray sandstone and siltstone remains from an ancient salt sea. Above the strip, some of the rock is gray-red claystone from freshwater.

The rocks date back 380 million years, but a more recent geological event prepped the area for Silver's project.

A glacier covered the site 20,000 years ago, leaving sand and clay when it receded.

In the years since, the Wapwallopen Creek blitzed a new course through soft, glacial remains. Three waterwalls hurtle down the stretch of the Wapwallopen that caught Silver's fancy.

"If it wasn't for the fact that the creek cut that, they never would have built the powder mill," Inners said.

The mill that Silver built diverted the creek's rage to waterwheels that turned machines.

When the creek flooded in 1858, however, Silver and a man to whom he sold a controlling interest in the mill, G.P. Parrish, went bankrupt.

E.I. du Pont de Nemours and Co. purchased the mill in 1859 for $35,000 and operated it until 1913.

Silver went on to form an infantry regiment for the Union army.

Du Pont, through the purchase, gained a powder mill closer to the anthracite mines that were major customers and farther from Confederate forces that threatened its mill in Delaware.

On one occasion during the Civil War, "two men, who proved to be disguised officers from the Southern army, were stopped within a half mile of the mills," B.G. du Pont wrote in "E.I. du Pont de Nemours and Company, A History, 1802-1902."

During the war, seven explosions of unknown causes occurred at the Delaware mill.

"Such catastrophes occur so much less often in times of peace, and are so helpful to the enemy in times of war that one hesitates to use the word 'accident' in describing them," du Pont wrote.

Under du Pont's ownership, the Wapwallopen mill expanded. Along a mile of the creek, buildings were spaced apart so an explosion in one wouldn't damages others. From the flume atop the gorge, channels rushed water to buildings housing machinery. The water spun turbines, which could produce up to 50 horsepower, compared with the 15 hp generated by Silver's waterwheel.

"That was an amazing amount of power. At that point, even steam engineers might have been 10 to 15 hp," John Ackerman, one of the engineers who toured the remains of the powder mill, said. "It's amazing what they were able to do with it."

Water-powered turbines rotated a pair of 8-ton wheels nicknamed the elephant. The wheels ground powder into small pellets that Civil War soldiers poured in their rifles or coarser pellets that miners used.

Without the creek, workers at the mill would have needed teams of horses to turn such large wheels. Yet today, Ackerman said a 50-hp motor just 2 or 3 feet long on a side could replace all the infrastructure that workers built along the creek to make gunpowder.

Gunpowder contains charcoal, sulfur that came from Sicily and saltpeter that the mill originally extracted from potassium nitrate shipped from India.

Workers made the charcoal by burning local birch wood in the charcoal house where a brick chimney more than two stories tall is one of the best-preserved structures still remaining at the former mill.

Two years before his family purchased the Wapwallopen mill, Lammot du Pont discovered how to produce saltpeter from sodium nitrate, a less-expensive raw material. Sodium nitrate was available in bat dung and animal urine from Chile and Peru.

Workers at the powder mill called saltpeter soda. Hall's book has a picture of workers standing outside the soda house where they refined the chemical by forcing steam through the raw materials.

"The smell must have been awful," Hall said.

Once the three ingredients were mixed, the substance became dangerous. Its explosiveness increased with each refinement as workers mixed, pressed, chipped, ground and dried the powder in different buildings.

Danger grew because the buildings weren't arranged in sequence with production so the product had to be moved more.

Hall learned the configuration of the mill just before closing time one day at the Hagley Museum. He found a map folded at the bottom of a box in the museum's archives.

Since then, Hall and his cousins made their own map showing approximately 50 buildings, three dams and multiple railroad trestles that cross the creek. They have started to mark the locations with a GPS device.

Horses that pulled the rail cars carrying product between buildings wore rubber shoes to avoid sparks. The horse-drawn railroad carried powder to the Susquehanna River where a ferry took the kegs across. From there, barges on the Susquehanna Canal, and later, railroads, carried away the gunpowder. On the railroad, empty cars separated cars carrying gunpowder from the rest of the train.

At the mill, workers prevented sparks by using wooden shovels when mixing and loading powder. They wore either rubber or felt-soled boots, or boots with wooden pegs rather than nails in the heels.

The men worked at least 10 hours a day - supervisors who did less manual labor worked two hours longer - and then walked home.

"So don't tell me you're tired," Hall said as his group prepared to re-climb the gorge during the tour.

He said many of the buildings had thick stone walls on three sides that could withstand explosions and channel the blast to a fly-away wall on the fourth side.

"If it exploded, the people were immaterial," Hall said. "The building costs were not."