Bigler's Rocks - Grampian, PA
N 40° 59.600 W 078° 35.590
17T E 702446 N 4540806
Bigler's Rocks are over 300 million years old. There is a parking area, picnic pavilion, hiking trails, Bigler's Run, and playground.
Waymark Code: WM14DHA
Location: Pennsylvania, United States
Date Posted: 06/17/2021
Views: 4
The creation of the sandstone seen exposed at Bilger's Rocks was during the Carboniferous Period that lasted from 354 to 290 million years ago. The rocks exposed at Bilger's Rocks are the Homewood Formation of the Pottsville Group, dominantly sandstone of Pennsylvanian age. These rocks were once covered by softer rocks (i.e. limestone & shale) that have been eroded away. In the vicinity of Bilger's Rocks the remaining sandstone bed measures over 50 feet thick and is broken up over hundreds of yards. The Homewood sandstone has an age range of approximately 316-320 million years old, predating the breakup of the ancient "supercontinent" known as Pangaea.
(from listed website)
The most striking feature about Bilger's Rocks are the various openings, crawlspaces, passageways, and arches found throughout the outcrop. These minute fissures and larger gaps are primarily caused by jointing within the rocks. Joints are caused by tectonic, or mountain-building forces that move and stress rocks, causing them to fracture. The resulting cracks provide an inlet for water, which slowly dissolves the rocks and allows space for ice crystals to freeze and thaw during the seasonal cycles, further pushing the rocks apart. Eventually, plants and trees also grow up through crevasses in the rocks and can exert considerable pressure as they grow, forcing even larger gaps to form. Gravity and erosion work together to slowly level the landscape by breaking the rock into ever smaller pieces and transporting it away.[3] The steady continental movement combined with relentless erosion and weathering over hundreds of millions of years has left the continually evolving "Rock City" that we can observe today. (from (
visit link) )