The Gritty Gravel of Governor Bridge EarthCache

This is an EarthCache, so it does not have a container or logbook. As you explore Governor Bridge Natural Area, you’ll discover how to tell natural gravel from crushed stone and see how the mining of gravel helped shape the landscape of the park. Permission for the cache has been granted by George Harley, M-NCPPC, Department of Parks and Recreation, Prince George’s County. The park is open from dawn to dusk only.

The Nitty Gritty

To log this EarthCache: Make observations at the three reference points and use the geology lesson to answer all the questions (1–4) below. Send your answers to me via the "Message the Owner" link above, or the “Send Answers” link in the app, do not post the answers to the questions in your log.

QUESTIONS:

1. Stream Bed (Point #1): Observe the stones in the stream bed, describe their color, size, and shape (round or angular). What does their shape tell you about how they were formed?

2. Lake Trail (Point #2): Examine the stone at your feet and compare it with those in the stream bed. Explain where you think this material originated from and whether it is natural gravel or imported crushed stone.

3. Roadway (Point #3): Observe and compare the color, size and shape of the stones at your feet with those at the previous locations. Explain why you think the material here is either local natural gravel or imported crushed stone.

4. What man-made and natural processes led to the formation of the ponds and lake?

Photo Requirement: Post a photo (face not required) of yourself or a personal item with one of the ponds clearly visible behind you to confirm your visit.

Bonus (Optional): Can you find any Patuxent River Stone? Describe its appearance (color, texture, patterns).

Suggested Trail Directions

This scenic loop covers about one mile and includes three observation points. Take your time and enjoy the natural beauty—feel free to explore additional trails throughout the park. Insect repellent is recommended during warm months. Trails are flat, but can be muddy after rainfall.

• Start at the parking area and choose either the Yellow or Red Trail. From these trails you can observe the smaller ponds. Continue until the Red Trail crosses over the Green Branch stream and intersects with both the Blue Trail and the Access Path. From this junction, follow the Red Trail eastward as it parallels the stream. After a short distance, there is access to the stream bed and Observation Point #1. 

• Return to the Red Trail and proceed straight on the Access Path to the Green Trail that borders the lake and find Observation Point #2. (You can observe the gravel anywhere in this section of the trail).

• Continue on the Green Trail to the access trail where it meets the Blue Trail and proceed to the gravel roadway for Observation Point #3.

• To return to the parking lot follow the Blue Trail roadway north.

The ponds and lake you see before you are manmade and serve as a visual reminder of a former gravel mine. They were formed from pits left behind after sand and gravel were removed sometime in the mid-1900s. The mine was abandoned in the 1960s, and the area was reclaimed in the 1980s.  

The Rolling Stones of the Patuxent

The gravel here began as crystalline bedrock high in the Appalachians. As glaciers moved and receded natural weathering and erosion carried bits of stone in rivers downstream here near the coast. They settled into broad, shallow terraces along the Patuxent River during the Pleistocene (about 2.58 million to 11,700 years ago) into what is geologically classified as the Quaternary Terrace Deposits. These sediment layers are among the youngest in Maryland and are comprised of unconsolidated (not cemented into rocks) interbedded (alternating layers) of sand, gravel and silt-clay. The stones and particles are typically tan, brown, or gray, and weathers to shades of yellow, orange, or brown, and are commonly limonitic. Limonitic soil contains a mix of different iron minerals that have oxidized (combined with oxygen and water to create rust) which gives the soil its distinct reddish color.

Among the rocks found here is Patuxent River Stone, Maryland’s official “gemstone.” This iron-stained quartzite occurs only in Maryland, and its vivid colors: orange, red, and white, echo those of the state flag. Look for translucent stones streaked or banded with rusty hues of red and orange along stream banks and trails.

Gravel Rocks!

Gravel is a loose blend of stone fragments of varying sizes, often combined with sand and occasionally clay. The precise meaning of gravel can differ depending on the region and its intended use. Geologists typically define it as loose, rounded rock particles larger than 2 mm (0.079 in) in diameter, often without setting an upper size boundary. While often grouped together as gravel, true natural gravel and crushed stone are different materials.

Natural Gravel is a type of sediment that forms through the weathering of bedrock, with quartz as its most common mineral due to its durability and resistance to chemical breakdown. Most gravel particles contain a mix of minerals and form naturally through the movement of water. As larger rock fragments roll or slide along stream bottoms, they collide and abrade one another, gradually smoothing their edges. These rounded stones then accumulate in stream channels, alluvial fans, coastal zones, and river deltas.

Crushed stone, by contrast, is a manufactured product, created by extracting rocks such as granite, limestone, or dolomite and mechanically breaking them into jagged fragments.

The key differences are in origin and shape: gravel is naturally formed and typically rounded, while crushed stone is man-made and angular.

Gravel vs. Crushed Stone

There’s Gold in Those Stream Banks!

Gravel may not be glamorous and sparkle like gold, but geologically and practically, it’s just as valuable in this region. Sand and gravel are the most abundant mineral resources in Prince George’s County.

Gravel forms the backbone of essential building materials such as concrete, asphalt, and mortar. It is used in everything from sidewalks and roads to homes and commercial buildings. Because importing gravel is often prohibitively expensive, locally sourced aggregates can be a real “gold mine,” helping to keep construction costs down while supporting the local economy. This demand has made gravel mining a major industry in the county for over a century.

Bank gravel in this area lies close to the surface, typically just beneath the topsoil. It’s commonly extracted through strip mining, a method that removes the upper layers to expose and access the gravel deposits below. This process alters the landscape dramatically by changing topography, disrupting natural drainage, and leaving behind pits and ridges.

The 1980 map above shows the location of the old, abandoned quarry here along the Patuxent River at Governor Bridge. The purple areas show the sand and gravel deposits. Black-bordered shapes mark large mining operations; crossed shovels indicate abandoned or inactive mines, while black triangles show reclaimed sites.  

Reclaiming old gravel mines helped restore damaged landscapes, reduce erosion, and make the land usable again for parks, housing and other community needs. After mining operations at this location ceased, the large open pits slowly filled with water, forming multiple ponds, the largest lake spanning 8 acres. The Prince George's County Parks Department acquired the land in the 1980’s. As part of the reclamation process, bare soil was seeded with grass to prevent erosion, a pollinator garden was planted to invite native species, and the ponds were stocked with fish. The site took many years to recover and is now a thriving natural area, but the land still bears visible signs of its mining past. As of 2018, 107 mines covering nearly 11,000 acres have been reclaimed in Prince George’s County.

You’ve sifted through the grit and mined some knowledge, thanks for visiting this EarthCache!