Environmental activists are pressuring the state to restrict Marcellus Shale drilling on 18,780 acres in a popular recreational area of northern Pennsylvania, where they say the state has a rare opportunity to control natural-gas extraction because of a 1933 deed restriction.

The Department of Conservation and Natural Resources is being pressed to put the brakes on gas development in the Loyalsock State Forest, where an exploration company has begun staking out drilling locations near the Old Loggers Path, a 27-mile loop trail that DCNR says "offers stunning vistas and clear, cold, cascading streams."

Six organizations, including Citizens for Pennsylvania's Future, say the state has rebuffed their requests to disclose drilling plans for the forest. They received no response from DCNR Secretary Richard J. Allan to a Sept. 7 letter calling on the agency to hold public hearings on the drilling plans.

"There is no precedent for holding a public meeting on a development plan," Chris Novak, the agency's spokeswoman, said in an e-mail. She said that no drilling has been approved for the disputed area in Lycoming and Sullivan Counties.

Anadarko Petroleum Corp., of Woodlands, Texas, which owns or leases the mineral rights under the forest, acknowledged that it had been in discussions with the state over developing the Loyalsock.

"DCNR has given us permission to perform preliminary survey studies, which includes staking the area to show where development locations could be and guide our environmental assessment of the area," Mary B. Wolf, an Anadarko spokeswoman, said in an e-mail.

DCNR itself has touted the area, which includes the Rock Run stream, as exceptional. "Few streams in Pennsylvania can match Rock Run's rich tapestry of deep, crystal-clear pools, cascading waterfalls and massive, weathered rock formations," an agency official said in a 2008 DCNR news release.

The environmental groups complain that DCNR's caginess reflects the Corbett administration's favoritism toward development of the Marcellus Shale, which the governor regards as the cornerstone of a rejuvenated Pennsylvania energy industry.

"This is kind of emblematic of the administration's approach to the public," said Richard Martin, coordinator of the Pennsylvania Forest Coalition, which has urged its members to write to DCNR's Allan.

Loyalsock State Forest lies above some of the most productive land in the Marcellus Shale, which has been generating a growing income for Harrisburg. About 725,000 of the state's 2.1 million acres of forests have been leased for gas development.

Marcellus Shale royalties quadrupled from $10.7 million in 2010 to $41.8 million last year. Through August of this year, the state has generated $41.5 million in royalties from Marcellus wells, matching last year's income in the first eight months of 2012.

But the state earns no royalties on 290,000 acres of state forest under which it does not own the mineral rights. That includes several substantial tracts of the Loyalsock.

The state typically would have little control over drilling activity on land where it does not own the mineral rights. Courts have ruled consistently that mineral rights trump surface rights - the sub-surface owner needs access to the land in order to mine or drill the minerals.

But environmental groups say that an unusual covenant in the deed to 18,780 acres of the Loyalsock gives the state uncommon power to control the surface activity.

In 1933, the Central Pennsylvania Lumber Co. sold the land to the state and kept the "mineral estate" for itself. The deed allowed the owner of the mineral rights access to the surface for 50 years.

In the 1980s, after the 50-year-provision expired, the state asserted that the mineral rights reverted to the state. But the Commonwealth Court in 1989 ruled that the mineral rights belonged to the current owner, a man named Clarence Moore. Moore still owned the mineral rights, but he no longer had surface access - the rights had expired in 1983.

The ruling was reaffirmed in 1999 by the Pennsylvania Board of Claims.

Moore later sold ownership of the mineral rights, which is now split between Anadarko and International Development Corp. IDC has leased its interest to Southwestern Energy Co.

Environmental groups discovered the provisions while researching the deeds in the Lycoming County Courthouse, said Ralph Kisberg, the president of the Responsible Drilling Alliance in Williamsport.

Mark Szybist, a PennFuture lawyer, said that the state could use the deed restrictions to force Anadarko to reduce the disturbance to the sensitive forests in exchange for surface access. Anadarko could also use horizontal drilling techniques to access the property from adjacent land it is leasing.

"We're saying these are public lands and the public should have a say in how those lands will be used," Szybist said.

DCNR says the issue is not open to discussion.

"It is DCNR's job to balance the many uses of our state forest lands, including recreational uses and mineral extraction," Novak said. "As you know, our state forests are independently certified as well-managed, and that acknowledges that we do a pretty good job balancing uses and protecting the future health of the public lands."

Anadarko says it, too, is mindful of the area's natural beauty.

"We recognize the importance of public lands in Pennsylvania, including the Loyalsock State Forest," said Wolf, the company's spokeswoman.

"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."

She said Anadarko would continue to work with DCNR and the state Department of Environmental Protection "to communicate approved plans as appropriate."

Contact Andrew Maykuth at 215-854-2947, @Maykuth on Twitter or amaykuth@phillynews.com.