Geology On the Trail

Feature photo by author; Mather Gorge.This gorge runs downriver from Great Falls. Steep walls funnel the Potomac River down to a narrow width. The relatively straight shape may be due to the Potomac following a fault line (fracture) and caused by progressive erosion as the falls dug backwards.

Article by FMN Stephen Tzikas

Geology is an inherent part of all trails. Some trails may have unique geological features.  However, all trails in Fairfax County and Northern Virginia share a similar geological history.  Virginia’s geology is that of orogeny, or mountain building, in more common terms. Virginia’s orogeny followed cycles. The Grenville Orogeny marked the amalgamation of the supercontinent Rodinia, about 1.3 to 1.1 billion years ago.  Rodinia’s rifting (i.e., breakup) began about 1 billion years ago.  So began a cycle, called the Wilson Cycle. The Wilson Cycle, or the cyclical opening and closing of ocean basins, can be explored at Great Falls Park.

After the Grenville Orogeny, there were three others.  The Taconic Orogeny commenced about 470 million years ago. This

Photo by author; Rock with Washington Plaque

orogeny involved volcanic island chains in the Iapetus Ocean, as the ocean next to Virginia was then called. At about 420 million years ago, the Iapetus Ocean had completely closed and the combined mass of land formed the new continent of Laurasia.  This was followed by the Acadian Orogeny about 390 to 360 million years ago. This orogeny involved a collision of Avalon with eastern North America.  Finally, the Alleghenian Orogeny occurred about 300 to 250 million years ago. This orogeny resulted from a collision between North America and Africa.  This orogeny was a continent-continent collision that formed the supercontinent Pangea. Following the Alleghenian Orogeny, the supercontinent of Pangea eventually rifted and the Atlantic Ocean was created. Why did it start with Grenville and not before?  Well, Earth up until then was a very active place with the process of plate tectonics and continental landmasses still in development.

Photo by author; Lamprophyre at the Great Falls Park Museum, formed during the Acadian Orogeny

At Great Falls Park one can find evidence for the deposition of turbidites from the Grenville Mountains into the Iapetus Ocean.  Turbidites are underwater avalanches which slide down the steep slopes of the continental shelf edge. These turbidite deposits underwent metamorphism and up thrusting into the rocks of Great Falls Park.  At one of the park’s landmarks, a rock with a George Washington memorial plaque is found. This rock has alternating layers of metamorphic mica schist and metamorphic metagraywacke turbidite deposit. More precisely, these were formed when sedimentary layers became destabilized and fell from the slopes of the continental shelf into deep ocean waters. These sediments were transported and deposited by density flow, not by tractional or frictional flow. That is, the coarser material settled first, the finer particulate matter followed.

Not as old as the turbidites, Granite too was push up unto the continent during the

Photo: Nanette Nyce, NPS website; Lamprophyre dikes in Mather Gorge. Yellow arrows point to dikes.

Taconic Orogeny.  In further orogeny events, the area of Great Falls was active with volcanoes.  About 360 million years ago Lamprophyre intruded into the fractures and dykes of older formations. The Lamprophyre rock was a volcanic igneous mica and feldspar and cooled upon reaching the surface.  Many of these rock types are on display at the Great Falls Park museum. The Lamprophyre Dikes can be seen near the head of Mather Gorge, just south of Rocky Islands.  They are a striking series of dark, vertical lines visible on both sides of the Potomac River.

When the last rifting occurred about 200 million years ago, faulting occurred as well as jointing.  The latter are fractures in rock, unlike a fault, which involves displacement. Joints can form due to cooling, shrinkage, or tectonic forces.  Jointing too can be as seen at Great Falls Park.  During this last phase rivers started flowing eastward again, sediments started flowing into the Atlantic, and the Potomac River may have started forming. About 3 million years ago the Ice Age began, and ice as high as 2 miles would cover NYC and Chicago. About 20,000 years ago, the ice age started thawing. While the Potomac was flowing during the ice age, its flow would begin to slow as its gradient would decrease as sea levels rose and further erosion of the Appalachian Mountains occurred.

27th Annual Eagle Festival, May 10th

 

Photo: Courtesy of Eagle Fest at Mason Neck State Park

May 10, 2025
10:00 a.m. – 4:00 p.m.

Mason Neck State Park,
7301 High Point Rd.,
Lorton, VA 22079.
Visitor Center Lawn

All events for the festival are free for everyone to enjoy!
Click here for additional information.

Join this full day of live animal shows, hands on educational opportunities, and outdoor recreation clinics that all aim to highlight the rich natural history of Northern Virginia and foster stewardship of our environment.

 See live wildlife up close

 Learn about our resident bald eagles and see them fly overhead

 Visit exhibits from our many conservation partners

 Enjoy live music, food, and more

Special thanks to the Friends of Mason Neck State Park for their continued support of the park and this event, and thanks to all our Peninsula partners and sponsors that make this event possible.

Parking for this event will be located off site and free shuttles provided to the festival. 

Spring Cleaning 🌳 Volunteer for a Watershed Cleanup! (April and May Dates)

A celebration of 10 years of the Fairfax County Spring Watershed Cleanup in partnership with The Nature Conservancy and Fairfax County Park Authority. It is time to come together with your community and neighbors to remove trash from your local waterways. Be a part of the solution—volunteers have removed nearly 30 tons of trash over the last decade through this spring cleanup!

Will you be one of the 400 people we need to pick up trash? Get your friends, family, colleagues, and groups involved.

Registration for the 2025 cleanups is open.

Event capacity is limited. Please follow instructions about registering in groups in the detail section of the registration pages. You can view a list of all park locations, dates, times, and number of volunteers needed here and below.

Saturday, April 19

  • Register: Merrybrook Run Stream Valley Park—9-11 a.m.
  • Register: John Byers Park—9-11 a.m.

Saturday, April 26

  • Register: Cub Run Stream Valley (Flint Lee Road)—9-11:30 a.m.

Saturday, May 3

  • Register: Lake Fairfax Park—10 a.m.-noon

Saturday, May 10

  • Register: Franconia Rec Center—9-11:30 a.m.

A confirmation email with additional details will be sent to registered volunteers about 3-5 days before the scheduled cleanup. If you have questions between now and then, please let me know. If the sites reach capacity, we encourage you join the waitlist and find additional opportunities to volunteer and connect with nature at:

Many thanks in advance for your help. We hope to see you there!
Happy cleaning,
Brynna

Brynna Strand
(she/her/hers)
Volunteer Coordinator
[email protected]

+1 540 255 5717 (Mobile)
nature.org

 

The Nature Conservancy In Virginia
652 Peter Jefferson Pkwy
Ste 190
Charlottesville VA, 22911 U.S.A.

Follow the Spring Bird Migration with the BirdCast Migration Dashboard!

Photo: Purple Martins, Keith Kingdon/Audubon Photography Awards

The new BirdCast Migration Dashboard provides summaries of radar-based measurements of nocturnal bird migration, including estimates of the total number of birds migrating, their directions, speeds, and altitudes. This tool depicts migration patterns in near real time or as a summary of a whole night after nocturnal periods end (2021-present); this includes additional historical information (2013-2021) as well as previous nights’ movements. Note that the dashboard currently provides data for counties and states in the contiguous US, complementing the existing forecast and live migration maps but allowing you to explore nocturnal bird migration in ways that were previously impossible. As your explorations begin, discovering interesting, new and previously unknown patterns will be, perhaps, the most exciting aspects of the new tool!

This tool presents a number of different measures of bird migration, and the descriptions below provide some basic information and guidance for interpreting these appropriately. Type in the county or state of your choice in the contiguous United States, select a date during migration seasons in 2021 or 2022, and begin! If you are new to BirdCast, get acquainted with the basics: How to use the BirdCast Migration Dashboard to experience your local migration in detail.

BirdCast is a consortium of interdisciplinary researchers, primarily from three organizations at present, with a growing list of collaborators, supporters, and partners.


Core Partners: Cornell Lab of Ornithology, Colorado State University, and University of Massachusetts Amherst
Core funders: National Science Foundation, Leon Levy Foundation, and Amazon Web Services
Other support: NOAA, US Geological Survey, National Fish and Wildlife Foundation, NASA, Microsoft
Other partners: Houston Audubon Society, Perot Museum, Dallas Zoo

 

 

Butterfly Gardening, Supply Side with Margaret Chatham, May 8th

Photo: Margaret Chatham, Virginia Native Plant Society – Potowmack Chapter

Thursday, May 8, 2025
7:00 pm – 8:30 pm

Virtual

Free – Registration required.

Margaret Chatham will discuss larval host plants for an array of local butterflies.

Margaret Chatham is a Fraser Preserve Volunteer Visitation Committee Member who removes invasive barberry shrubs in winter and wavyleaf grass in summer and knows the preserve intimately. She is also editor of the VNPS Potowmack News newsletter, a volunteer at the VNPS propagation beds at Green Spring Gardens in Alexandria, and an Arlington Regional Master Naturalist.

Clean the Bay Day, June 7th

Saturday, June 7, 2025
9:00 a.m.-12:00 p.m.

This short, three-hour annual event has a massive cumulative impact. Since the event began in 1989, this Virginia tradition has engaged more than 165,500 volunteers who have removed approximately 7.18 million pounds of debris from our land and waterways.

The 36th annual Clean the Chesapeake Bay Day event takes place on Saturday, June 7, 2025, from 9 a.m. to noon at sites all across the Chesapeake Bay watershed in Virginia. Volunteer registration will open in April. If you would like to be contacted when registration opens, join the email list.

Clean the Bay Day could not be the huge success that it is without everyone joining together and lending a hand. Check out the photo album. Watch the video to see why so many people participate.

Ready to go one step further? Each cleanup site needs a Zone Captain. It’s easy! You simply check in volunteers and report back data. Webinar training and other resources will be provided. Contact us at [email protected] if you would like more information.

In 2024, more than 3,680 volunteers and 60+ CBF partners gathered at over 200 sites across Virginia. Thanks to their hard work more than 82,200 pounds of debris were removed from parks, beaches, rivers, streets, and lakes.

Spring 2025 Native Plant Sales

Photo: Courtesy of Plant NOVA Natives

Why Native Plants?

  1. Naturally beautiful! Native plants will add beauty to your garden. Not convinced?

  2. Made for here! Native plants are adapted to local conditions. Planted in the right place, native plants need less water and other care than our non-native lawns. 

  3. Good for the Earth! Unlike non-native plants such as turfgrass, native plants support butterflies, birds and pollinators AND healthy water!

If you are looking for particular plants, in most cases you can contact the vendors ahead of time to ask them to bring them for you.

Friends of Riverbend Park – Saturday, April 5


10:00am

Friends of Riverbend Park Bluebell Sale
Riverbend Park
8700 Potomac Hills Street
Great Falls, VA 22066
Bluebells will be sold on the deck of the Visitor Center in conjunction with the Bluebell festival

 – and –

 Saturday, April 12
10:00am

Friends of Riverbend Park – Pickup for Native Plant Sale
Riverbend Park Educational Pavilion
8700 Potomac Hills Street|Great Falls, VA 22066
For presale of native plant orders and details, go to Friends of Riverbend Park

 

Walker Nature Center Native Plant Sale – Saturday, April 12

Saturday, April 12
9:30am-1:00pm pickup

Walker Nature Center Native Plant Sale
11450 Glade Drive
Reston, VA 20191

Pre-orders are due by March 28 at 5pm.
Online form for pre-orders is available.
See [email protected] for other details.

 

Town of Vienna Conservation and Sustainability Commission Native Plant Sale –  Saturday, May 3


8:00am-12:00pm

Town of Vienna Conservation and Sustainability Commission Native Plant Sale
Vienna Community Center
120 Cherry St.
Vienna VA 22180
Vendors include Hill House Farm & Nursery

 

Walker Nature Center Spring Festival –  Saturday, May, 3

1:00pm-5:00pm
Walker Nature Center Spring Festival
11450 Glade Drive
Reston, VA 20191
Features native plant vendorNature by Design

 

Green Spring Gardens Spring Plant Sale – Saturday, May 17

9:00am-3:00pm

Green Spring Gardens Spring Plant Sale 
4603 Greensprings Rd
Alexandria  VA 22312
Native plant vendors include Hill House Farm & Nursery and Seven Bends Nursery

Early Spring Blooms for The Garden

Photo: Plant NOVA Natives

Article by Plant NOVA Natives

Our woodlands and meadows are about to awaken and burst into a vibrant display of spring ephemerals, the transient native beauties we love to see, especially after the cold and snowy days of winter. They are among the first spring plants to emerge and are indeed ephemeral. They don’t last long, completing their life cycle in a matter of weeks to take advantage of the sunlight that filters through the canopy before the trees leaf out.

Virginia Bluebells are a well known and popular example of a spring ephemeral, celebrated during Bluebell festivals around the region in April. But the show starts earlier, with Spring Beauty sprinkling  the ground starting in late March, followed by a whole array of fascinating species including Trout Lilies and Dutchman’s Breeches. We can bring their splendor and interest to our homes by planting them in our landscapes and gardens. They are the native equivalent of crocuses and daffodils, a difference being that they are transplanted in pots rather than planted as bulbs.

The blooms of spring ephemerals are small and delicate, almost fairy-like in appearance, and yet they are an important source of early pollen for newly emerging bees. Our gardens can serve as a haven for these small but mighty plants that directly support the biodiversity of the region. Spring ephemerals will emerge before many of us begin to actively garden, so successful cultivation requires some advance thought and planning. They need sun in late winter and early spring but require shade later on as the sun intensifies and temperatures rise. They will be at home in most woody settings on your property, so plant them under trees, shrubs, and other large perennials where the soil is moist. They are particularly charming along paths and walkways where you can enjoy them every day as you pass by. You can read about them on the Plant NOVA Natives website.

Some growers advise that early fall is the best time to plant spring ephemerals, but the plants are harder to find for sale then since they would just look like empty pots. Planting them in the spring is just fine, but you may not see blooms in the first season. Most commercial nurseries these days sell the more popular species of spring ephemerals such as Virginia Bluebell, but a wider selection of species can be found in the native plant nurseries and at the local spring native plant sales.

Please remember this important rule when considering spring ephemerals for your property. You should always buy them from a grower and never take them from the wild. They are slow to propagate and will likely die if you disturb them. They may be small and short lived, but they are crucial to the native ecosystems and a testament to the renewal of spring. Let’s enjoy them in the wild where they have decided to plant themselves.

Before this year’s spring ephemerals come and go, it’s worth the effort to get out and see them sprinkled across wetlands and woodland floors in parks and other undisturbed preserves across Northern Virginia. They are a sight for sore eyes after the drab gray of winter. Open your plant identification apps, grab your native plant guidebook, or go on one of the spring ephemeral walks such as the ones hosted by the Virginia Native Plant Society. Watch your step and stay on the paths as you take in the wonderful display. Get to know them, fall under their spell, and you will no doubt be inspired to purchase and plant several of these magical beauties for your own garden viewing pleasure.

Building Resilient Soil for a Changing Climate with Dan Schwartz, April 10th

Photo: Dan Schwartz

Thursday, April 10, 2025
7:00 pm – 8:30 pm

Via ZOOM

Free – REGISTRATION IS REQUIRED

Dan Schwartz is a Soil Scientist with the Northern Virginia Soil and Water Conservation District. He is a member of the soil survey update team and provides soil information to the public and agency staff. He also helps organize county-wide watershed clean-ups in the fall and spring.

City Nature Challenge – Washington DC Metropolitan Area, April 25th – May 4th

Image: citynaturechallenge.org, Washington DC metro area

Friday, April 25 – Monday April 28, 2025 take photos of wild plants and animals

Tuesday, April 29 – Sunday, May 4, 2025 identification of what was found

Do you like observing nature? Make your observations count! The City Nature Challenge is an adventure in metropolitan areas worldwide to discover and identify wildlife. You will be looking for signs of life in parks, neighborhoods, and backyards to see what plants and animals share our environment. Join the City Nature Challenge and become a citizen scientist!

Everyone in the Washington DC metropolitan area with access to a camera and the internet can observe wildlife for the Challenge. Anyone worldwide can help with identifying your finds!