Geology Hikes

Geology Hikes Leave No Stone Unturned
By Barbara J. Saffir
Special to The Washington Post
Reprinted from The Washington Post 10/5/01

Every rock has a story. And geologist E-An Zen can entice you with their tales. Especially the epic saga of Mather Gorge, arguably our region’s most spectacular natural landscape.

The saga begins at the Fairfax Stone, a marker erected in Tucker County, West Virginia, to mark the source of the Potomac. When the river reaches Great falls, it drops 76 feet in elevation over a distance of only 3,500 feet, roaring over jagged rocks at more than a million gallons a minute. Just south of the falls, it has carved out Mather Gorge, a six story canyon wall of roughly 600-million-year-old rocks.

Through most Washingtonians probably don’t realize it, "the Great Falls started out in Georgetown," Zen explains. It retreated to its present location, about five miles outside the Beltway, hundreds of thousands of years ago. "In the process of retreating it developed the gorge," he says. The falls migrated because of "drilling" and "quarrying," the removal of large blocks by floods and by abrasion, two processes still going on today.

Zen and other geologists who lead tours of the Great Falls area delight in pointing out evidence of those forces, particularly the terraces and potholes that perplex many hikers on the northern Billy Goat Trail, the rugged path atop the Maryland edge of the Potomac. The terrace that the trail runs along is actually an ancient bottom of the Potomac River before it cut a deeper channel into the bedrock. The smooth cylindrical potholes were caused by swirling currents grinding pebbles against the rock when it was still underwater.

"You can go there and see things changing almost in real time," Zen says. "Most geological processes are so slow. You can look at a mountain all your life and it won't change. But at Great Falls, you see boulders being moved by flood."

"You get a lot of bang for your buck going a short distance," adds Paul Tomascak, a University of Maryland scientist who brings geology students there on field trips. That’s because hikers see an exposed view of the fall line, the drop-off from the Piedmont Plateau- with its hard, crystalline rock base- to the soft, sedimentary underbelly of the Atlantic Coastal Plain.

Although many hikers and kayakers are lured there by the rapids and the spectacular cliff-side setting the geology creates, few nonscientists understand their origins. This is one reason the National Park Service started offering public geology hikes. People want to learn how the land under our feet was formed, says Rod Sauter, a supervisory ranger who has led the hikes himself. "It’s a fascinating story, " Sauter says, and Zen explains it in a "great engaging style… he has the knowledge and the means to communicate to people who don’t have the knowledge," he adds. "That’s a rare combination."

Zen, 73, helped train some of the other local geologists who lead the hikes. He started the walks because of his own curiosity. When he retired 12 years ago, after earning his PhD at Harvard University and working for three decades at the U.S. Geological Survey (USGS), he wanted to learn more about the processes that formed Mather Gorge, named for the National Park Service’s first director. Each hike "is kind of a progress report" on his story, he says. And each walk is different, depending on the questions people ask.

The walks attract everyone from preteens to physicists. Even honeymooners are enthralled by his tales. On one jaunt, a young couple cozying up to each other along the C&O towpath overheard Zen as he was leading a tour. "They got so interested, they stayed with us the rest of the trip," Zen says.

Zen leads three different walks around Great Falls: one that concentrates on the boardwalk area around the actual falls, another that starts at the north end of the Billy Goat Trail and his favorite, a mile-long excursion beginning north of Great Falls and winding up at an outlook just before the Billy Goat Trail on Bear Island. After the public tour, hikers can independently scramble along the entire Billy Goat with their newfound knowledge. Park rangers also lead a history-focused hike along the strenuous two-mile trail, from its start near the Rocky Islands to Cupids Bower, or Sherwin Island, as it’s called on some maps.

Before trekking to the park, experts recommend picking up "The River and the Rocks: The Geologic Story of Great Falls and the Potomac River Gorge." The 75-page hiker’s bible describes a self-guided geology tour of the Billy Goat Trail and features photographs of many rocks, including mica schist, the predominant rock in the cliffs.

Some of the rocks near Great Falls are craggy and gray while others appear smooth and black. Still others are cut with thick veins of white quartz, some of which conceal bits of gold. Zen and his fellow guides relish explaining why they look that way, unlocking the mysteries of almost every boulder, pebble, rock and stone.

For more information and a schedule of future geology and Billy Goat Trail hikes, please call the Great Falls Tavern Visitor Center at (301) 767-3714.