Paper No. 3
Presentation Time: 9:00 AM


TIPTON, Brian, Department of Geography/Geology, University of Nebraska at Omaha, 6001 Dodge Street, Omaha, NE 68182-0199,

Granitic erosional residuals known as pedestal or mushroom rocks occurring in Vedauwoo State Park, Medicine Bow National Forest, WY, possess a wide variety of atypical flare orientations. Various polygenetic influences within the immediate study area have produced these mushroom-like formations. Intense climatic variations on the Sherman granite erosion surface have a large influence on the weathering front of the granite. Cataloguing the pedestals using various photographic methods, GPS, Google EarthTM and profile comparisons have allowed us to determine their non-preferential direction of weathering within the joint sets of the area. Excavation and exposure of several pedestal bases were completed on numerous features to examine the depth of bedrock relative to the present-day surface. The objective was to expose any other potential subterranean basal flares or bed rock connected to the pedestal. The supportive columns were significantly lighter in color relative to their lichen-covered tops suggesting faster weathering rates than the cap above. Accumulation of moisture containing salts in the surrounding regolith can produce extreme chemical weathering in and around the pedestals. Frost wedging from water penetrating into the rock mass primarily by way of open fracture thought to be a possible source of subaerial micro fracturing. Exposure to moisture can therefore enhance the subterranean rotting of biotite into clays, weakening the rock into residual feldspar and quartz clasts (grus). Old plain surfaces originally located at widest points of the upper caps have progressively lowered over time from water and wind erosion. The formation of pedestal rocks is likely episodic over an extremely long period of time rather than a particular mass wasting event. Spalling as well as anthropogenic influences were also observed throughout the area, although not thought to be a major influence on formation.