The boulders of Hammonds Rocks, in Pennsylvania’s Michaux State Forest, are literally ancient history. But they explain a good bit about the present, too.
Michaux State Forest, and the South Mountain ridges on which it rests, is a landscape first formed by shifting continents, later by the blaze of iron furnaces and then the stewardship of state foresters. It’s an epic chain of custody, linked by the movement of rocks and minerals, that gave birth to a forest, which was in turn pillaged, then restored.
Geologist Sean Cornell, a professor at nearby Shippensburg University, uses Hammonds Rocks as an outdoor classroom of environmental change. “You can go back 540 million years and see that record here on the mountain,” Cornell said.
The walk to Hammonds Rocks is very short, if you travel to the northern end of the forest by car and park in the small pull-off area near the rocks. Ridge Road will have already carried you to the crest. The rocks seem to spill down the slope, and the higher you climb, the taller and more numerous they grow. They are rippled, grooved and streaked. Many angle sharply toward the sky.
Clamber onto the highest “tower” — once used as a fire watch station — and you’ll glimpse the valley sprawled below. While you’re feeling on top of the world, take a moment to ponder the rocks beneath your feet. They are the remnants of a subtropical shoreline, formed more than 500 million years ago on a land mass that geologists know as the supercontinent Rodinia.
When the old continents began to shift and collide, oceans rose and drowned rocks like these, which had been deposited at the mouth of rivers. Then the land began to rise and fold. Cornell compares it to shuffling cards by pushing them into an A-shaped peak.
“If you cut off the top of the peak, you can see the lowest layers near the top,” Cornell said. “At Hammonds, the top of the rocks are cut off. So it shows us these lower, older rocks.”
Fractures formed in the rocks as they rose, like gaps between cards in the flexed deck. What happened next set the stage for more recent history: The fractures were filled.
“When the Atlantic formed and rifted Africa away from North America, there were magma chambers,” Cornell said. “All that water had to go somewhere. It traveled through those fractures, and it carried metals.” In some places, like South Mountain in Pennsylvania, the process created massive veins of iron.
Long after North America formed and rotated, moving what would become South Mountain into its current position in south-central Pennsylvania, the veins were mined for iron ore at such a frenetic pace that it transformed the mountain once again. Settlers created forges in the 1700s, and production was industrialized during the 1800s.
Ironmaking required three things: iron ore, limestone and charcoal created from burned timber. South Mountain provided iron ore and a huge forest. Limestone was located at its base.
Ironmakers mixed the ore with limestone in a tall stone furnace fed by charcoal; the chemical reaction burned off impurities or “slag” in the ore. Chunks of blue-green slag can still be found on the grounds of Pine Grove Furnace State Park, where a large iron operation once stood.
Molten iron was drawn from the furnace and cooled into small bars for sale and transport. The line of iron bars in the cooling mold resembled piglets next to a sow and were known as “pig iron.”
Furnaces consumed hundreds of acres of trees every year. Young trees were harvested quickly because they burned more easily into charcoal. Nothing was replanted. When the iron works fell out of use in the late 1800s, a ravaged mountain was left in its wake. Local residents had almost no incentive for restoration.
Craig Houghton is a forestry professor at Penn State Mont Alto, located at the southern end of Michaux State Forest on the site of a former iron company. “Forest land was taxed at a very high rate, so people would cut it down. It was repeatedly cut over and burned over, and forests were not growing back,” Houghton said.
When the state began to buy the land, there was little forest left, and almost none of it was healthy. Visitors today might have a hard time believing that, because Michaux State Forest alone includes more than 85,500 acres, almost entirely wooded — and that’s not counting the forested acreage of Caledonia, Pine Grove Furnace and Mont Alto state parks, or the Kings Gap Environmental Center — each of which share the mountain with Michaux. The Appalachian Trail is a forested corridor across the spine of the mountain, and its vehicular counterpart, PA Route 233, travels heavily shaded roads that contrast greatly with the developed strips and interstate nearby.
The state forest was named for Andre Michaux, a French botanist who traveled the area in the late 1700s and was stunned by the devastation he saw when he returned a few decades later. Michaux willed Pennsylvania $12,000 at his death in 1855 to promote better forest management.
Roy Brubaker, district forester for Michaux, has a practiced eye for healthy forests and said that the recovery there is still not complete. The regrown forest lacks its historic diversity of trees, and some wildlife species, like grouse, are declining because of it. Still, much credit for the initial reforestation can be traced to a state forestry school that was established on the former grounds of the Mont Alto Iron Works.
The Pennsylvania State Forestry Academy, founded in 1903, was the first professional forestry program in Pennsylvania and only the second in the nation. Among the first graduating class, in 1906, was Ralph Brock, who is considered the nation’s first African-American forester.
The academy was absorbed by the state college, now Penn State University, in 1929. Students fought the change. “It was not well-received,” Houghton said. “It was considered a hostile takeover.”
But the School of Forestry moved forward, using the state forest as its training grounds. Its work impacted Michaux as well as the nation: Twelve graduates from 1929–63 became state foresters in locations across the county.
The modern forest of South Mountain faces new challenges, but it is a delight to visit. Michaux offers primitive camping. Caledonia and Pine Grove Furnace state parks offer campgrounds with amenities. A portion of the Pine Grove iron furnace still stands, and the former ironmaster’s mansion is now a hostel. You’ll find small quiet lakes, several overlooks, and more than 60 miles of marked and unmarked trails, plus the Appalachian Trail. Secluded streams host native brook trout. Mountain biking is popular, as well as hiking, horseback riding and ATVs.
Growing recreational demands have challenged land management in Michaux, which can be reached in two hours or less from Harrisburg, Baltimore and the District of Columbia. As a state forest, instead of a state park that prioritizes recreation, the land is preserved for multiple reasons: ecosystem benefits like water quality and wildlife habitat; limited timber harvest; and public use. As hikers and cyclists spill from state parks to explore the forest, and large group events are on the rise, trails and signage in some areas are not well-developed or protective of sensitive areas.
Brubaker’s mission is to balance these uses. “We need people to understand the high bar we’ve got to meet if we want to reach our ecological goals,” Brubaker said.
To help visitors, forest managers are completing a trail study and updating maps. They are also increasingly designing projects for shared benefits. Some timber harvests are simultaneously helping to restore barrens habitat on the ridges. Other cuts, like salvaging the remains of dying hemlocks, make more space for a variety of appropriate species.
At Hammonds Rocks, the Pennsylvania Parks and Forests Foundation has led a large effort to remove graffiti from the stones, clean up litter and install a sign. The restoration project, supported by Brubaker's staff, Cornell's students and many community volunteers, has also raised awareness about the site's important history and the need for on-going stewardship. Soon, tree clearing along the ridge will help restore the barrens habitat and reveal an expansive view. Connecting trails might be created. “It’s one of the nicest outcroppings in the forest, but it’s not really connected to anything else,” Brubaker said.
To plan a visit to South Mountain in Pennsylvania, explore the Michaux State Forest website. It’s a good hub for maps and information about trails, overlooks and state parks. You can also call the Michaux office at 717-352-2211 or stop by to ask for maps and advice. Another option is more personal.
“One of the best ways to get to know Michaux is to come with someone who knows it,” Brubaker said.