Geologic History 

Sedimentary rocks constitute the majority of rocks that are present at shallow depths in the Pike Run watershed. Sedimentary rocks form as a result of the weathering of pre-existing rocks and sediments. Primarily rivers transport the weathered products of rocks (gravel, sand, silt, clay, and dissolved ions) and deposited where they lithify (or harden) to become rocks with time and pressure by deep burial. Some examples include sandstone, siltstone, and shale. The sedimentary rocks in the Pike Run watershed were primarily deposited in rivers and shallow, ancient marine environments.
Bituminous coal deposits underlie western and north central Pennsylvania. The mineable coals, "mostly of Pennsylvania age, are interbedded with shale, siltstone, sandstone, and the occasional limestone,"( Brady and others, 1998). The bituminous coal-beds lie with in the Appalacian Plateaus Physiographic Province and is characterized by gently dipping strata; nearly horizontal coal-beds commonly crop out in the incised stream valleys.
Approximately 570 million years ago (during the Cambrian period), Pennsylvania was located near the equator. The warm sunny waters were conducive to deposits of carbonate rocks such as limestones and dolomites. A similar environment of carbonate deposition occurs today in the Florida Keys and the Bahamas in the Gulf of Mexico. With the shifting of the plates underlying the continents, the eastern margin of North America began to collide with a volcanic island chain, approximately 430 million years ago. This event is comparable to the movement of the island chains of the South Pacific Ocean moving towards Australia. The collision of the island chain into North America caused crust to be folded and uplifted to form the mountains in eastern Pennsylvania. The increase in elevation resulted in increased erosion of the mountains and an increase in the weathered rock particles. These particles were transported westward by rivers where they were deposited and lithified to form sedimentary rocks. Other collisions with continents occurred during the Devonian period, approximately 405 million years ago, and again in the Permian period, 290 million years ago. Mountain building and, then erosion characterized each of these collisions. The erosion of mountain building caused a large supply of sediments to be transported westward into present day western Pennsylvania and Ohio forming sedimentary rocks of the Ordovician, Devonian, and Permian age.
The most recent Orogenesis (mountain building) episode was the Allegheny Orogeny occurred during the Permian period and is responsible for the Appalachian Mountains. The Appalachian Mountains were formed when by the collision of eastern North America and Africa. The continent to continent collision was responsible for the formation of the Himalayan size-mountains in central Pennsylvania. The modern analog to this event is the collision between Indian and African Plates forming the Himalayas Mountains. Following this final mountain building episode in the Permian, eastern North America was characterized by erosion of the landscape from the Jurassic period (250 million years ago) through the Cretaceous Periods (67 million years ago). During this time, North America also separated from Africa to form the present day Atlantic Ocean. Continued erosion occurred during the Tertiary time period is thought to be responsible for the creation of much of the landscape in present-day Pennsylvania. (R. Vargo)