EXPLORING THE GEOLOGIC HISTORY OF SOUTH-CENTRAL PENNSYLVANIA FROM GOVERNOR DICK TOWER

Governor Dick is a 351-meter hill located in south-central Pennsylvania just east of the town of Mount Gretna. An 18-meter observation tower on the hill provides outstanding views with features up to 80 kilometers away clearly visible on a good day. The location at Clarence Schock Memorial Park presents an exceptional outdoor opportunity to observe and discuss the geological history of south-central Pennsylvania, including the sedimentological, tectonic, and structural record of the Taconic, Acadian, and Alleghenian orogenies, Mesozoic rifting, Cenozoic uplift, and landscape evolution.

From the tower at Governor Dick, visitors can see terrain that represents a billion years of Earth’s history. The high hills and ridges of the Piedmont Upland physiographic section to the east and southeast are held up by Precambrian basement gneisses overlain by basal Cambrian clastic quartzites and shales. To the south, the broad, level valleys are underlain by Cambro-Ordovician carbonate rocks and the hills are underlain by shale. To the far south the resistant early Paleozoic schists hold up a high ridge. To the north the Great Valley is underlain by Cambro-Ordovician carbonate rocks and heterogenous association of shale, quartzite, limestone, and metavolcanic rocks. On the north side of the Great Valley, the Valley and Ridge Province is characterized by a series of three resistant ridge-forming Paleozoic quartzites with shales, siltstones and minor limestones in the valleys. Blue Mountain ridge is the prominent landmark. Governor Dick is in the Mesozoic rift basins (Gettysburg-Newark Lowland) and is held up by Jurassic diabase and hornfels of Triassic conglomerate and sandstone.

More in-depth discussion can cover topics including the development of passive and active margins, sedimentary basins, flysch and molasse sedimentation, structural nappes, thick-skinned versus thin-skinned tectonics, continental rifting, and the intrusion of diabase sills.