Dinosaur Rock, Lebanon County


Location: Lebanon County, Elizabethtown 7.5-minute quadrangle; on State Game Lands 145;
40º 13' 42.3" latitude and 76º 30' 19.9" longitude. Decimal degrees: 40.22843, -76.50554.

Size: The boulder area covers about an acre.

Photo of Dinosaur Rock, approximately 30 years ago.
 

Geology: This outcrop is an erosional remant of an igneous rock called diabase. During the Jurassic period in southeastern Pennsylvania, a large mass of molten rock cut upward into Triassic sedimentary rocks. Subsequent erosion of rocks allowed these resistant rocks to form some of the highlands of the piedmont. The diabase is composed mostly of minerals plagioclase feldspar and pyroxene. Crystals of plagioclase are enclosed with pyroxene crystals, which give it a texture called “ophitic.” This indicates that as the magma slowly cooled, plagioclase crystals formed first. The boulders are spheroidally weathered, and their presence was probably influenced by the colder climate of the last glacial age.

The remnnant of diabase still stands approximately 15 feet higher than the surrounding woods. A profile of the rocks from the north or south reveals a form that gives the outcrop its name—“Dinosaur Rock.”
Dinosaur rock, plagued by graffiti.

Another view of Dinosaur Rock.

Heritage value: Site is scenic and educational. Displays an erosional remnant, the weathering of diabase boulders, and a whimsical shape of a dinosaur.

Heritage status: Site is potentially threatened, especially by graffiti.

How to get there: Dinosaur Rock is located in southern Lebanon County, along Mt Wilson Road (Route 3005), just north of where it crosses the Pa. Turnpike (there is no access from the turnpike). Park at the State Gamelands 145 parking area, which is on the east side of Mt Wilson road and 0.7 miles south of Mt. Gretna Road in Colebrook. From the parking lot, cross Mt Wilson Road to the trail to Dinosaur Rock. Follow the trail about 500 feet to the diabase rocks.

Accessibilty and safety: Easy walking though cars travel fast along Mt Wilson Road, which must be crossed from the parking area. Path is fairly smooth and flat but would be rough for a wheelchair. Ample room for large groups. Rocks may be slippery; climbing is not recommended. No public toilets.

Map showing the site location.

Facilities: No facilities are available. Colebrook is the nearest town, approximately 3/4 of a mile north on Mt Wilson Road.

Reference: Outstanding Scenic Features of Pennsylvania, A. R. Geyer and W. H. Bolles, 1979, 508 p.

For information regarding geologic features and PNHP, contact Jim Shaulis of the Pennsylvania Geological Survey at 717–702–2037.