Here are some of Mercer County's key natural areas outlined in the Mercer County Natural Heritage Inventory:

   » The Barrons Heronry in Sugar Grove Township along the Little Shenango River is the largest great blue heron rookery in Pennsylvania, with about 500 nests in black cherry and tall sycamore trees. Herons are generally moving west, and have abandoned nesting sites such as the Brucker Sanctuary in West Salem Township. The easily spooked birds enjoy seclusion.

   » Mercer Bog in East Lackawannock Township contains a 140-square-meter floating mat peat vegetated primarily by few seeded sedge, cranberry, pitcher-plant, three-way sedge and cotton-grass. Robert Coxe of the Western Pennsylvania Conservancy, which conducted the inventory, said you can jump up and down on the mat and it will make waves. Frequent visitation could harm the mat, but the property owner has said he wants to protect the bog and surrounding habitat.

   » The wooded areas of Brandy Springs Park, Mercer, are home to the American columbo, a plant that flowers only once in about seven years, then dies. The plant is sensitive to disturbance and invasive plants.

   » Barmore Lake on the property of the Grove City Country Club, Pine Township, is once again home to Pursh's goldenrod, which had not been chronicled at the site since 1922.

   » The Open Sedge Fen in Sandy Creek Township contains no invasive plant species, which is rare in Mercer County.

   » Pine Swamp in Worth Township contains the only raised bog in Pennsylvania. The bog covers about 60 acres. The area was once a shallow lake that formed in a glacial depression. Organic matter collected in the lake producing a mass of peat. The center dried and contracted producing a raised center. The bog is home to three rare or imperiled plants, short awn meadow foxtail, broad-leaved water plantain and bog bluegrass.

   » The Shenango River below New Hamburg still has "scars" of the Erie Extension Canal, which now serve as backchannels to the river. Fish and mussels that generally would stick to old oxbows -- deep bends in a waterway -- have found the calmer water of the backchannels to their liking.

   » French Creek in French Creek Township would be considered the county's top natural resource if it wasn't in such a small part of the county, about 1è miles in the northeast corner. But, the area is rich in unique natural features and is the home of seven endangered or imperiled fish or mussels and a plant, the head pondweed. A slope near Deer Creek has scattered, exposed boulders, which you won't find anywhere else in the county. Another notable feature is small glacial kettle holes that were created from ice blocks left on the valley floor as the glaciers retreated during the last ice age.

   » Sandy Lake is the only glacial lake in Mercer County and one of only eight major ones in western Pennsylvania. While eastern glacial lakes are acidic, the western ones are high in alkaline, and each type fosters a different kind of natural life. Mine drainage in the 1800s killed off much life in the lake, but the area around the lake is home to 11 rare or imperiled plants, including the small flower foxglove in the forested sections, lesser tussock sedge and meadow willow in the shrub swamps and water bulrush and bushy naiad in the lake.

   » Kashner Corners Swamp in Otter Creek Township, a headwater tributary of Otter Creek, is a wet meadow. Communities of wide-leaved cattail, rice-cut grass, reed canary grass, nodding sedge, great bladder sedge and other plants are identifiable by their shadings of color.