The 14 parks of the National Capital Region (NCR) lie within the Atlantic Coastal Plain, Piedmont, Blue Ridge, and Valley and Ridge physiographic provinces. The geologic history of the region has been both dynamic and varied. The region's history includes the collision of continents, volcanism, rifting to form new oceans, the rising and falling of ocean levels, and powerful erosive processes. These processes have produced a modern landscape that is not only interesting in geologic terms, but that also provides a wide range of resources and ecological niches.
The Geology & Soils Program at the Center for Urban Ecology (CUE) identifies and describes significant geological and soil features within the parks of the NCR. Because the region's geologic and soil structures have been altered by development, the protection of soil resources associated with land use is a primary goal. The Program provides technical support to park managers for regional land use planning and resource management and protection. CUE partners with local and national programs, notably the Geological Society of America’s GeoCorps program, to provide support on issues including air quality, stream ecology, paleontology, and geological resources.
The geologic history of the NCR is primarily connected with the formation and erosion of the Appalachian Mountains.
Approximately 600 million years ago, a rift tore apart an ancient supercontinent. Volcanism associated with this rift left behind widespread igneous rocks.
The rift created a basin that was filled by an ancient ocean called the Iapetus. This ocean preceded the Atlantic, and is named after the mythological father of Atlantis. The Iapetus Ocean grew larger as the rift spread the fragments of the fractured supercontinent farther apart.
The National Capital Region is divided into four different areas, or physiographic provinces, based on geologic features:
- The Coastal Plain province contains sediments from the erosion of the Appalachians.
- The Piedmont holds metamorphosed seafloor and rift deposits from when Pangaea broke apart.
- The Blue Ridge rocks are the core of the Appalachian Mountains.
- The Valley and Ridge province holds marine and terrestrial deposits that were deformed into valleys and ridges during the Alleghenian Orogeny.
Eventually the Iapetus Ocean began to close, and three different land masses collided into the continental margin of what would become the east coast of North America. These collisions triggered several mountain-building episodes, termed “orogenies” by geologists, which together formed the supercontinent Pangaea and the Appalachian Mountains.
First, between 440 and 420 million years ago, a string of volcanic islands collided with the coast, driving up mountains in an event called the Taconic Orogeny.
Second, a land mass that was approximately the size of Japan collided with the continent during the Acadian Orogeny, which took place approximately 360 million years ago.
Finally, a massive collision with the ancient African continent occurred during the Alleghenian Orogeny, which took place between 325 and 265 million years ago. This collision completed the formation of Pangaea and pushed the Appalachian Mountains to heights rivaling the modern Himalayan range.
Pangaea was later broken apart during rifting that occurred during the Triassic (~251-201 million years ago). Africa and North America separated, and the Atlantic Ocean was formed.
Explore the formation of the Coastal Plain, Piedmont, Blue Ridge, and Valley and Ridge provinces by clicking the links in the sidebar.