We care, because we all leave tracks.

Geologic History

The land that is now within the four square mile, southern Sugarland Run watershed, including Runnymede Park, has had tremendous changes and forces applied to it over the millennia. Continental drift, tectonic rifting and uplift, magma intrusions, volcanism, sedimentation, glacial activity, and erosion have all played a part in the formation of the land that now rests in Runnymede Park. A review of these conditions over the geologic time scale is listed below to give an idea of the changes that took place in this park before the arrival of the first humans. The abbreviation MYA is used to indicate Million Years Ago, and YBP is used for Years Before Present.

600-530 MYA: The earth had cooled from its early formation about 4.6 billion years ago and oxygen had been generated into the atmosphere from early single celled life forms. Multi-celled plant and animal life had become established in the oceans. The area of the park at this time was under a Cambrian ocean, known as the Iapetus Ocean, between land forms that later disappeared as geologic forces worked on the tectonic plates underlying this area. The ocean had micro-organisms floating in the currents with early arthropods beginning to appear as simple crustaceans and more complex trilobites roving the aluminum and iron rich sediments looking for detritus settling from the ocean above.

530-490 MYA: The area of the park thrust above the ocean level. This land mass is known as Laurentia, or proto-North America. The aluminum and iron rich sediments from the earlier period were now metamorphosed by intrusion force and heat to create hard rock rich with the mineral staurolite, the state mineral of Georgia. You can find outcroppings of rock faces with this twinned crystal staurolite today in Fairy Stone Park outside of Martinsville, in southern Virginia. There were no land organisms as the atmosphere and the geologic activity on the surface had not yet allowed the conditions for life to leave the oceans. Constant acid rainfall from the sulpher rich atmosphere and plate thrusting worked upon this land mass area. During this time, the park’s area of Laurentia was actually below the equator in the southern hemisphere and facing more south than east.

490-430 MYA: A mountain building period known as the Taconic orogeny occurred through continental collision of a micro-continent known as Avalonia into Laurentia, creating much of New England. This period began the creation of the Blue Ridge Mountains and further metamorphosed the area’s underlying rock to form metagraywacke and schist rock that can be seen today at Mather’s Gorge in Great Falls Park. A huge intrusion of granodiorite schist rock was thrust to the surface a few miles east of this area. Today you can see the remnants of this rock formation with fine biotite and muscovite mica crystals at Bear Island, just below the falls on the Potomac River. Metagraywacke at Great Falls

The global temperature was generally 10-20 degrees warmer than present.

430-136 MYA: Many forces worked upon this land. About 350 MYA North Africa collided with Laurentia. Laurentia and other land masses eventually collided together to form the super-continent of Pangea by 306 MYA. This entire land mass was slowly moving into the northern hemisphere through this time period. By 200 MYA Pangea had separated to create the continents that we know today. Over the course of the next 200 million years, plate tectonics would shift these continents into their current positions. These forces caused the area of the current park to be thrust into a small mountain range, and then trapped it under an inland, freshwater lake separated from the ocean by a mountain range. It became land again as the lake filled in with sediments from the weathering away and deposition of the surrounding landscape.

The first land plants appeared around 400 MYA and the first amphibians appeared on land around 350 MYA. The global temperature cooled dramatically starting about 345 MYA to temperatures more like today, then rose back again to the earlier warmer climate about 230 MYA when a mass extinction occurred that killed off 90% of the ocean species in an event known as the great Permian extinction. During this cooler time known as the Carboniferous (345-280MYA) and Permian (280-230 MYA) Periods land-life flourished with large ferns, trees, amphibians, and reptiles diversifying and expanding to eventually create the coal seams and oil deposits found today north and west of this area in Pennsylvania. The first dinosaurs and small mammals began to appear 200 MYA following the Permian extinction.

During the Triassic (230-190 MYA) and Jurassic (190-136 MYA) Periods, igneous magma (heated, liquid rock) welled up creating heat and pressure in these sediments to form various sandstones, siltstones, and shale. Dinosaurs (meat eaters and plant eaters) once roamed this area as evidenced by tracks that have been found in Stevensburg, Manassas, and along Little River at Oak Hill, VA in this sedimentary rock formed from this period.

Dinosaur footprint from Stevensburg, VA displayed at USGS Reston headquarters

There are no fossils from this period in the park as the sedimentary rock was melted and deformed (metamorphosed) by the intrusion of igneous diabase rock that filled cracks in this sediment. You can see these diabase rock dikes and sills exposed in several parts of Sugarland Run, particularly from the central to the south end of the park (see photo below). Many of these rocks were gathered from nearby and used to construct the Carroll Cabin in the early 1900’s.

Diabase intrusion at Sugarland Run in Runnymede Park

This diabase rock is rich in magnesium and as it weathered, it has created magnesium-rich soils in the park. The black sand that can be found along Sugarland Run came from the weathering of this hard diabase rock. These soils rich in magnesium (and calcium) support unique and highly diverse plant communities.

136-1.8 MYA: The beginning of this time found the area of the park in a cooler global climate and plate tectonic shift that brought the area of the park very near the edge of the Atlantic Ocean (which was created with the splitting of Pangea). Dinosaurs, mammals, reptiles, fish, and birds all flourished during this time known as the Cretaceous (136-65 MYA) Period. The first flowering plants appeared on land. The global climate warmed up again from about 100 – 25 MYA. The park area slowly got farther away from the Atlantic Ocean as erosion of the surrounding landscape deposited its material along the shore creating sedimentary rock and gravel pits that can be found in places north and east of the park. A mass extinction occurred to end the Cretaceous Period around 65 MYA, many theorizing today that it was caused by the impact of a 10 mile wide meteor crashing into the Gulf of Mexico. Dinosaurs became extinct, mammals became a more prominent life form, and the first grasses began to grow on the landscape.

Near the end of this time, known as the Tertiary (65-1.8 MYA) Period, the ocean just off shore teamed with life including the largest meat eating shark that ever lived, the Carcharodon megalodon. This shark ruled the oceans with hundreds of constantly replaced serrated teeth up to 7½ inches long and a body length of over 70 feet, three times as large as the great white shark of today’s oceans. A large scallop lived in the ocean sediments near the shoreline whose fossils were described in a scientific book in 1687, making it the first fossil illustrated in America. See photos below for samples of these fossils:

Chesapecten jeffersonius>Carcharodon megalodon tooth>

The now extinct scallop fossil, Chesapecten jeffersonius, named in 1824 after the Bay and one of the state’s leading naturalists, is today Virginia’s state fossil. Four to five million year old fossils of Chesapecten and teeth of Carcharadon can be found today in various spots along the Chesapeake Bay, including Westmoreland State Park near Montross, Virginia, and Calvert Cliffs in Maryland. By the end of this period, the climate became steadily colder and the Pleistocene epoch began 1.8 MYA.

1.8 MYA-15,000 years before present (YBP): During this Pleistocene epoch, great glaciers formed and created ice sheets that carved much of the Cretaceous and Tertiary deposits off the landscape along the eastern seaboard up to the fall-line represented in this area by Great Falls on the Potomac. There is some debate as to exactly when and how the Potomac River that the Sugarland Run feeds into was formed, but it created several terraced landscapes along its course during this period as the glaciers advanced and receded. The area of the park was just west and south of the area carved by most of the glaciers and the flow of the Potomac River during this time. It has been assumed that some of the remnant plants found around the Maryland side of Great Falls and the Dranesville District Park were carried (seeds, spores, and bulbs) here by the glaciers from areas much further north. No evidence has been found of man living in this area during this time.

15,000 -11,000 YBP: It has been theorized that glacial activity created a land bridge (by lowering the sea level 300 feet) across the Bering Straits from Siberia to Alaska that allowed man to travel across and eventually spread south and east to populate virtually all of North and South America. These men, known as Paleo-Indians, were hunters who followed their prey and gathered the fruits, vegetables, and grain from the native land that they needed to survive. They made beautifully fluted stone points, chipped from flint and chert that they hafted (attached with sinew or fiber) onto wood shafts to create spears to hunt with. The earliest of these points in America, dating to around 13,000 YBP, were named Clovis and Folsom, after the towns in New Mexico where they were first found.

There is some evidence that this land bridge may not have been the only one that man traveled across, as a site known as Meadowcraft near Pittsburgh, Pennsylvania has produced evidence of man living there before this land bridge opened, including a woven basket carbon-dated to 19,600 YBP.

After being present for over 1,000 years, the last land bridge over the Bering Straits closed with the warming of the climate beginning 12,000 YBP, once again separating North America from Asia. By the very end of this time, glaciers were just 500 miles north of the park.

Deer of the Park