This is a park and earthcache. Pull into the parking pullout at GZ, then view the fields across the intersection. You are on a country road (MD 68) so you have a great calm view.
This earthcache highlights a unique feature of the carbonate rock in the Great Valley.
Logging Requirements:
Send the answers to #1-#3 to me through my geocaching profile. DO NOT post the answers to any logging requirements on this site.
- List the name “GC**** Pinnacles Outcrop Earthcache” in the first line of your email. This is done automatically if using Message Center.
- Which direction are the pinnacles all leaning? (North, East, West, or South)
- What approximate percent of the landscape is pinnacles? Grikes?
- (optional) Post a picture of yourself and/or your GPS with your log that shows you at the GZ.
I will only respond if you have incomplete logging requirements. Go ahead and log your cache
Geology:
This rock formed in a carbonate bank in an ocean in Cambrian and Ordovician time. If you are just driving through ad not making stops, one carbonate feature you can observe in fields is the uneven features of GRIKES and PINNACLES. Grikes are steeply dipping fractures or bedding planes that have been dissolved and filled with soil through many years of weathering. Protruding bedrock outcrops in between the relatively level soil areas are called pinnacles. Fields with many pinnacles are used for pasturing rather than planting (for obvious reasons).
This region is part of the Rockdale Run Formation, where the limestone weather NEARLY uniformly, leaving NEARLY flat fields, except for pinnacles of more resistant limestone – pinnacle outcrops. Because limestone dissolves differently when it reacts to precipitation (weathering), small fractures can become underground channels of subsurface drainage. Soil forms in the dissolved depressions, leaving pinnacles and grikes. In the region, the pinnacles become dominate because of tightly folded layers of the Rockdale Run limestone. The “tilted” very-tightly folded folds crack, then get weathered, leaving the pinnacles and creating the grikes. (other earthcaches go into detail about types of weathering so we will not do that here - though the same principles apply.)
Rockdale Run limestone is actually composed of both dolomite and limestone, and contains some algae fossils. It is part of the Beekmantown Group, of Ordovician time period.
Resources:
Means, John. Roadside Geology of Maryland, Delaware, and Washington, D.C. Missoula, Montana: Mountain, 2010. Print.
Schimidt, Martin F. Maryland's Geology. Atglen, PA: Schiffer, 1993. Print.