Brook Lenker aimed the van along a dirt road that wound though a narrow valley filled with hardwood trees that had gone largely undisturbed for decades. Waterfalls poured down the mountainside in places, and hemlocks provided a touch of green along streams as leaves of other trees adopted their autumn orange and yellow hues.

This was part of Loyalsock State Forest, which covers 114,494 acres of northcentral Pennsylvania. Much of the land was bought from the Pennsylvania Lumber Company in the early 1930s after it had logged the area. Shortly thereafter, the Depression Era Civilian Conservation Corps set up several camps in the area to reclaim the land and the forest.

Today, its expansive woodlands provide critical habitat for forest-dwelling birds; its clear streams draw anglers in search of brook trout; and popular trails cross its valleys and plateaus, including the Old Loggers Path, one of the state's most popular long-distance trails.

Lenker pulled the van to a stop and led a small group down a wooded slope to what many consider one of the Loyalsock's greatest gems — Rock Run.

Upstream, water cascaded through narrow slots in the rock, finally pouring into a large bowl where freshly fallen yellow and orange leaves swirled around. Ultimately, the water would flow out of the rock bowl, through the forest to Loyalsock Creek, and eventually make it to the Chesapeake Bay.

"I've heard Rock Run referred to as the prettiest stream in Pennsylvania," said Lenker, executive director of the FracTracker Alliance, a nonprofit organization that operates the FracTracker website, which allows people to monitor drilling activity.

Lenker was leading a tour with several other conservationists to highlight forest and wildlife issues related to natural gas drilling. But the calm around Rock Run, several warned, is deceiving.

Members of the Loyalsock Creek Watershed Association, the Pennsylvania Forest Coalition and the Responsible Drilling Alliance recently began finding stakes with red-and-white banners on the plateau to the north. The stakes were marked "APC," the initials of Texas-based Anadarko Petroleum Corp., which has been actively drilling for natural gas in the region.

The headwaters for Rock Run are in the seeps and wetlands on the plateau, and local conservationists worry that any drilling there could forever change what the state considers an "exceptional value" waterway.

"If an accident were to happen, we could have serious damage to the stream," said Steve Szoke, a member of the watershed association and an avid angler who has fished the stream's trout for years. "Absolutely I'm worried about it," he added.

Szoke and others believe the state has a unique opportunity to protect Rock Run and a sizable chunk of Loyalsock State Forest, although they are worried the Department of Conservation and Natural Resources, which manages the Loyalsock and other state forests, will not exercise its authority on the matter.

Pennsylvania owns about 2.2 million acres of state forest land, about 1.5 million acres of which lies above the Marcellus Shale formation, which holds one of the largest natural gas reserves in the nation. New drilling techniques that allow companies to reach the deep gas deposits have brought a drilling boom to the region, with more than 5,000 wells drilled to date — a number expected to grow more than tenfold in the next couple of decades.

Former Gov. Ed Rendell initially promoted drilling in the state forests to help fill the state's cash-starved coffers with royalty payments. From 2008 through 2010, the Rendell administration opened 138,866 acres of state forest above the Marcellus Shale to leasing, generating $413 million in revenue.

Foresters warned that opening additional lands to drilling would endanger the environmental quality of the forests and threatened outside certification that the state forests are being sustainably managed. That certification adds value to Pennsylvania's $6 billion forest product industry.

In October 2010, four months before leaving office, Rendell signed an executive order imposing a moratorium on opening additional state forests to drilling. He cited the need to conserve "the most significant tracts of undisturbed forest remaining in the state. Failing to protect these acres will significantly alter the ecological integrity and wild character of our state forest system."

But the moratorium only protected unleased areas where the state retained ownership of underground mineral rights. On lands where private parties own those rights, the state still has to provide "reasonable use," and its ability to regulate drilling activities is greatly restricted.

As a result, the moratorium protects only about 800,000 acres of state forest land above the Marcellus Shale, while about 700,000 acres are open to drilling, either because they have been leased, or because the state does not own oil and gas rights.

A patchwork of mixed mineral rights ownership lies under much of the Loyalsock. That's because while Pennsylvania Lumber Company sold the land to the state, it sold the mineral rights to others. The state ultimately acquired some rights, while rights to other tracts were bought by others and have been bought and sold over the years.

But groups working to protect Rock Run say an unusual deed restriction gives the state DCNR an opportunity to restrict development on 18,870 acres of the Loyalsock where the state does not own mineral rights, including a portion of the Rock Run headwaters.

The mineral rights to that tract were once owned by an attorney from the District of Columbia named Clarence Moore. The wording in the deed contains an unusual restriction in which the right of the mineral rights owner to access oil and gas from the surface was terminated after 50 years — in 1983.

This 50-year limitation on surface access was challenged by Moore, but upheld by Commonwealth Court in 1989 which concluded that "access subsequent to March 28, 1983, is controlled by the Commonwealth." That conclusion was upheld again by the state Board of Claims in 1999.

The mineral rights are now owned by Texas-based Anadarko Petroleum Corp. and International Development Corp., the latter of which has leased its interest to Texas-based Southwestern Energy Co.

Environmentalists say the deed restriction allows the state to greatly restrict drilling activity on that tract, or even require that it be accessed only through horizontal drilling from outside areas. But the discovery of Anadarko's stakes and flags marking apparent drilling sites has worried conservation groups that the DCNR is ceding its ability to regulate what happens on the surface.

"It makes me think they (DCNR) may have already bargained away the state's rights — or are ignoring the Commonwealth Court's decision and taking the position that the state doesn't control the surface," said Mark Szybist, a staff attorney with Citizens for Pennsylvania's Future (PennFuture).

In a letter to the DCNR Secretary Richard Allan, conservation groups contend that the state would need to specifically grant a right-of-way to Anadarko to work on the surface, but it cannot do so under state law if the right-of-way would "so adversely affect the land as to interfere with its usual and orderly administration." The letter contends drilling would likely adversely affect Rock Run, a state-designated exceptional value stream.

In addition, the letter stated, the DCNR needed to show how "the interest of the Commonwealth or its citizens will be promoted" by such a right-of-way.

Because the state does not own the mineral rights, it would not get royalties from the drilling.

The letter, dated Sept. 7, expressed concern about the recent seismic testing on the lands, and asked the DCNR to clarify what activities it was considering.

The DCNR never responded.

Christine Novak, a spokeswoman for the DCNR, acknowledged that seismic testing to determine what reserves lay beneath the ground had taken place in parts of the forest, as it has on other state forest lands. But she said no decisions have been made about what activities would be allowed.

"Specific to this area, there is a complex combination of publicly and privately owned surface and subsurface rights, so at the moment there is no definitive answer about what will occur in the future," Novak said in an e-mail. "As the law applies, DCNR cannot prohibit access to subsurface mineral rights it does not own, but we do work proactively with the owners to balance the interests of all users of the forest."

Representatives from Anadarko did not return calls for comment, but a spokeswoman recently told the Philadelphia Inquirer that "we recognize the importance of public lands in Pennsylvania, including the Loyalsock State Forest. As with all of our operations, and in particular on state forest land, we are looking to minimize surface disturbance and protect special places like Rock Run."

Szybist said he believes the state is trying to make the ownership issue sound more complex than is the case to justify allowing access to the disputed tract. The Loyalsock is in a hotspot for natural gas drilling — almost 70 percent of the state's natural gas production comes from the four counties that surround Loyalsock State Forest. Szybist, along with other environmentalists, say the DCNR is reflecting the friendly approach to gas drilling taken by the administration of Gov. Tom Corbett.

"We've heard that the state is afraid of being sued by Anadarko. But the state's legal position is so strong, they shouldn't fear that at all." Szybist said. "I suspect that the state's apparent willingness to cooperate with Anadarko has other motives."

Environmentalists say there are ample reasons to put the brakes on drilling activities in the Loyalsock. With drilling taking place in many privately owned forests, remaining unleased areas of state-owned forests provide the greatest opportunity to preserve the natural character of Penn's Woods.

A report by The Nature Conservancy last year estimated that between 100,000–240,000 acres of forest will be cleared during the next two decades to make way for drill pads, pipelines and other drilling-related infrastructure.

In the Bay watershed, potential forest loss is estimated at 45,000 to 110,000 acres. (See "Marcellus Shale drilling may take huge chunks out of PA forests," November 2011.) That has the potential to increase sediment and nutrient runoff to the Chesapeake over the long term, and in the short term impact habitats for brook trout, which are a priority species for the Bay Program. The draft federal Chesapeake Bay 2013 action plan directs federal agencies to explore the impact of Marcellus shale drilling on brook trout.

Scientists and EPA officials have indicated any increased nutrient and sediment runoff from drilling activities would need to be offset with reductions elsewhere to meet, and maintain, pollution limits set in the Chesapeake Bay Total Maximum Daily Load, or pollution diet.

Critics say drilling in the Loyalsock would ruin the experience of hiking the popular 27-mile Old Loggers Path which winds through the area and draws hikers from as far as New England because of its spectacular scenery.

The plateau where the drilling may take place also harbors several rare plants.

Narrow, sparsely traveled state forest dirt roads, barely wide enough for two vehicles to pass, would have to be widened to make way for heavy truck traffic. "Picture the current width of this road essentially doubled," said Lenker, as he drove through a narrow valley next to a stream. And, he cautioned, the increased traffic on the roads is likely to spread harmful invasive plant species to the interior of the forest.

Stopping by an old CCC camp, established to repair damage caused by an earlier era of forest exploitation, Paul Zeph, director of conservation with Pennsylvania Audubon, said the spider web pattern of forest clearing created by pipelines, widened roads and drill pads would be particularly devastating for forest birds.

The Loyalsock is designated as an Important Bird Area by the Audubon Society because its large hardwood tracts provide refuge for interior forest-dwelling birds such as the scarlet tanager, wood thrush, black-throated warbler, black-throated green warbler and acadian flycatcher. The Loyalsock supports particularly high numbers of each of those species, which winter in the tropics but migrate north to take advantage of the springtime explosion of insects and caterpillars to provide food to successfully rear their young.

These birds often nest on or near the ground in forests that once provided them safety. As forests are fragmented by drill pads, roads and pipelines, the birds become vulnerable to predation by blue jays, raccoons and other species that live along forest edges, but venture short distances into the woods to forage. The more woodland is fragmented, the less "safe" interior habitat is left for forest-dwelling birds, and their populations typically plummet as fragmentation increases.

"If their habitat is lost, they can't just go somewhere else and make a nest," Zeph said. "This is the only home that they have, and if they can't nest here, then they will be unable to nest in Pennsylvania, and their populations will begin to diminish.

"This is such an important place that we cannot believe the state would allow this to be fragmented and the natural resources that live here to be impacted," Zeph said. "There are not very many places like this that are so precious in Pennsylvania."