A lumpy, round-shouldered ridge of sand and stone deposited by melting glaciers during the last Ice Age is the target of a mining proposal in western Butler County and a battleground for the rural way of life.

The six-mile-long Jacksville Esker, a 23,000-year-old glacial formation 40 miles north of Pittsburgh, is the best esker left in Pennsylvania, and a destination for hikers, birders, scouting expeditions, geological researchers, and university and high school field trips.

"This esker is a special geologic feature and part of the essence of Pennsylvania that we need to preserve," said Ruth Roperti, president of the Pennsylvania Association of Environmental Educators and executive director of the Moraine Preservation Fund.

In 1973, the Western Pennsylvania Conservancy bought a 32-acre patch of the low ridge, now known as the Miller Esker Natural Area, to preserve a small rocky remnant left from when two-mile-thick glaciers sheeted the northern half of the state.

Glacial Sand and Gravel, a subsidiary of Kittanning-based Snyder Associated Cos., has filed an application with the state Department of Environmental Protection to strip mine 44 acres on a 77-acre tract it purchased next to the conservancy property at the eastern end of the esker.

The permit application asks for variances to allow mining within the 100-foot road buffer required by state regulations and to encroach on Black Run, a cold water fishery and tributary of Slippery Rock Creek.

The mining company also wants to build a stone washing and preparation plant on the site that would receive materials from some of the eight other properties it owns and eventually wants to mine in an area rich in glacial sand and gravel deposits.

Mark Snyder, an owner of Glacial Sand and Gravel, said the former farm tract contains about 2 million tons of sand and gravel. An average of 80 truck trips a day -- more in the summer -- would move the sand and gravel from the esker mine site the company has named Mine 47, and from other mining operations, into and out of the prep plant. Most of the material would be used for road building.

"The esker is made of sand and gravel and mining sand and gravel is an important part of our business, so mining this formation is a logical thing for us," said Mr. Snyder, who hopes to open the prep plant in November and begin mining in March 2009.

But the DEP hasn't approved the mining permit yet. And residents of the mostly rural but fastest-growing county in the western half of the state seemed divided at a public hearing that attracted 150 people to Slippery Rock High School's auditorium last week.

"The mining laws and DEP will make sure the mine will not cause any harm," said Carol Miller, whose family sold the esker land to the Western Pennsylvania Conservancy 35 years ago. "Placing a [prep] plant and mining won't damage the conservancy land. The loss of revenue and the rights of the land owner should be considered."

Carl Rogers, who sold the property on the esker to the mining company, said the esker has already been chopped up by a road and some smaller gravel quarries.

But for others, the Jacksville Esker, also known locally as the West Liberty Hogback, is close to sacred ground -- it may contain Native American burial sites -- and is an important link to the environmental and cultural history of the region.

An esker forms when melt water drains into a glacier through fractures and flows through ice tunnels at its base. The sand and gravel deposited by the melt water along the tunnel form an elongated ridge that stands above surrounding ground level when the ice melts.

The Jacksville Esker is approximately 50 to 70 feet above the surrounding countryside.

The state Department of Conservation and Natural Resources has identified it as one of the outstanding scenic geological features in Pennsylvania and is reviewing whether to list it as a state biological diversity area.

Drew Orient, who has visited the esker with his son's Cub Scout troop, said the proposed mine would damage the esker, nearby wetlands and rural roads. The mining also may run contrary to land use provisions in a recently adopted Northwestern Butler County Multi-Municipal Comprehensive Plan.

"Mining is a competing use with natural areas and the agricultural and rural communities," Mr. Orient said. "We really need to preserve the unique natural aspects of our state."

Marian Hollinger, who lives across the road from the mine site and owns 50 acres, including part of the esker and man-made Tamarack Lake at the site of a former glacial pothole lake, said the mining would damage the springs that feed West Liberty Bog, an "exceptional value" wetland, and dry up the lake.

She also is worried about how turtles that migrate across a road between the bog and lake in the spring will survive the truck traffic.

"There's an area of the road known as 'turtle alley,' " she said, "and with the tri-axle trucks rolling through every three minutes, they're not going to last very long."

Michael Tudor, who lives nine miles away from the mine site, said permitting the mining would cause serious fragmentation to the rural landscape and result in loss of biological diversity. He urged the DEP to review the permit application with an eye to the cumulative effects from existing and planned mining in the area.

"In the past the effects were less noticeable, but now there are more and bigger developments and the cumulative impacts take hold," he said. "I'm here today to try to protect a way of life in a habitat worth saving."

Jane Cleary, president of the Citizens Environmental Association of the Slippery Rock Area, requested that DEP conduct an environmental impact study and a truck traffic study and hold another hearing once those are completed.

Lori Odenthal, chief of technical services and permits for DEP's northwest region, said the initial permit review completed in December identified 52 deficiencies. The company has asked for an extension to address those shortcomings.

Because the Pennsylvania Natural Diversity Index has identified the West Liberty Bog as a potential site for an endangered plant, the mining company must find and hire a biologist to survey the area. Ms. Odenthal said she didn't know when the survey will be done.

The public comment period on the mine permit application is open until March 4. Comments can be mailed to Javed Mirza, Knox District Mining Manager, P.O. Box 669, Knox, PA 16232, or e-mailed to lodenthal@state.pa.us