Click on a numbered square to see description along that part of the trail. Trail guide provided by Natural Bridge State Park with permission of the Park Naturalist.
1. Shaft-cave opening.
Just past the point in the trail where the Balanced Rock Trail connects to the Original Trail, or just up from the stairs on the trail from Hemlock Lodge to the Original Trail, there is natural cave opening (to the left of the Original Trail). The opening is a short shaft, which descends into a cave. It is very steep and slippery, and easy to fall into: USE CAUTION WHEN APPROACHING. The cave occurs in limestones of the Slade Formation, just beneath sandstone cliffs of the Corbin Sandstone Formation. After a rain, water that hits the top and slopes of the ridge enters the thin soil that covers the ridge. When the water passes through the soil on the ridge slopes it becomes slightly acidic. The sandstone bedrock beneath the soil is permeable. This means that water can pass through it. The water travels through fractures and through microscopic spaces between individual sand grains in the rock. The water travels within the sandstone until it reaches the limestones and shales of the Slade Formation. These units are not permeable. The water starts to build up along the contact until it finds a fracture or weakness in the limestone, as shown in the picture. Because the ground water is slightly acidic, it can dissolve the limestone forming shafts and caves.
This particular shaft may have been part of a pit and dome. Pits and domes are common cave features in Kentucky. In this case, the dome has been eroded leaving only the pit, which descends into the cave below.
2. Sandstone cliff
When you get toward the final ascent on the trail, there is a bench, and the trail makes a sharp turn to the left at the base of a steep rock cliff. The rock in the cliff is composed of sandstone and conglomerate. If you touch the cliff you can feel the gritty or sandy texture of the sandstone. Sandstone is composed of sand-sized grains. When the sandstone contains pebble-sized grains it is called conglomerate. Look closely at the cliff and you can see many white pebbles. The pebbles are composed of the mineral quartz. For that matter, so are the sand grains in the sandstone.
Sandstones and conglomerates are types of sedimentary rocks. Sedimentary rocks were originally deposited as sediments. This unit of sandstone forms conspicuous cliffs all along the Cumberland Escarpment, and is called the Corbin Sandstone. The straight edge of the cliff is formed by a natural fracture.
3. Sandstone bedding
Looking down the trail along the cliff edge, the bedding within the cliff wall is highlighted. Layers of sandy sediment formed the horizontal lines across the cliff, which were deposited one on top of the other in an ancient stream. This type of bedding is called crossbedding. These crossbeds were deposited as sand bars in the ancient stream. The pebbles within the sandstone were transported along the bottom of the stream when it was flowing.
Sediment in the stream was deposited during the early Pennsylvanian Period, more than 315 million years ago! At that time, the sediment that now is the rock in the cliff, was being deposited at the bottom of a broad valley (different than the valley today). Movement of the earth along faults, and erosion during the millions of years since the ancient river sediment was deposited has left the sandstone up on the valley wall more than 400 feet above the present river level.
4. Iron Staining-Nature's Art
If instead of passing directly under the arch, you start sideways along the ridge toward Battleship Rock, you will come to a beautiful exposure of iron staining in the cliff wall less than 100 feet from the arch. These types of curving, ornate, deposits of iron are called Liesagang bands. They are formed when iron and manganese in ground water precipitates on a cliff surface. At this location, a fracture may have aided water movement.
5. Natural Bridge
Natural bridge is a natural arch. There are several types of arches in the Red River Gorge area. If you look down the valley on either side of the bridge, you can see that both valleys meet at the bridge. The convergence of two valleys on opposite sides of the ridge is how this natural arch was formed.
The diagram above, is a cross section, or vertical slice through the ridge at Natural Bridge. The diagram shows how the arch may have formed. The ridge in which the arch occurs is highly fractured (1). Fractures are oriented parallel to the length of the ridge where the arch occurs. Through time water in the valleys on either side of the ridge eroded deeper into the ridge, but also upwards into the ridge (2). Most of the time, creeks on either side of a ridge, do not meet at the same place at the top of the ridge. In those cases, arches don't form. But when the ridge is eroded in the same spot on either side of the ridge, an arch can form.
Formation of the arch is also related to fractures in the ridge. If you look at both sides of natural bridge you can see that the rock on the sides of the bridge is very straight. That is because the bridge occurs between two parallel fractures at the top of the ridge.
As water on either side of the ridge, eroded the slopes away, slabs of rock broke away along parallel fractures (3). It may help to imagine opening a book, binder side down and letting the pages fall away from the middle of the book. Slabs of rock fell away along the fractures in a similar way, until only the center of the ridge was left (4-6).
Ultimately, the streams on either side of the present arch eroded back to the level of the last two prominent fractures (6). At that time they began to undercut the ridge, probably forming rock shelters on either side of the ridge (7). Subsequently, erosion connected the two shelters to form an arch. Vertical erosion to the present shape of the arch closely follows bedding, so that erosion appears to have broken off slabs of crossbeds upwards.
6. Plant fossil in sandstone
Several sandstone blocks line the trail beneath Natural Bridge. Some of these contain fossils of logs that were once wood carried in the ancient streams that formed the sandstone.
7. Fat Man's Misery
The narrow trail in the rock up the backside of the arch, is a natural fracture in which steps have been carved to get to the top of Natural Bridge. Through time, the fracture will widen, until one day in the distant future, the rocks on the outside of the fracture will fall away down the valley. But don't worry too much, these things take a long time (thousands of years)
8. View toward Lookout Point
From the top of Natural Bridge you can look out to other parts of the ridge top, including Lookout Point. USE CAUTION ON TOP OF THE BRIDGE! AN ADULT SHOULD ACCOMPANY CHILDREN. THERE ARE NO GUARDRAILS AND YOU WALK ACROSS AT YOUR OWN RISK. The top of the bridge is a natural trail and is wide enough to traverse. If you cross the bridge you can walk to Skylift, or the Lookout Point Trail.
9. Top of the ridge sandstone
If you don't wish to travel down the same trail you came up, you can take the Balanced Rock Trail. This trail connects to the Original Trail (you just traveled) below where the cave-shaft opening was. The Balanced Rock Trail has several steep staircases. It is much better to travel down this trail then up. But if you don't like steep descents, avoid this trail, and return on the Original Trail.
On top of the ridge, the sandstone is exposed to the elements. Commonly, rain, snow, and ice, cause the sandstone to weather into rounded or smoothed shapes.
10. Steep stairs
The park service has built a series of stairs to get up and down the steep cliff walls on this side of the ridge. There are several steep stair cases along the Balanced Rock Trail, which is why it is recommended to descend from Natural Bridge, rather than ascend to Natural Bridge, along this trail.
11. Rhododendron gardens
Along many parts of the Balanced Rock Trail, the slope is in the shade all year. The shady slope, sandy, and slightly acidic soil are perfect for rhododendrons. At many points along the trail, the trail has to be cut through a virtual forest of large rhododendrons. These plants bloom in mid-May through early June.
12. Sawtooth fractures in the cliffs
If you look at the cliffs at the base of the trail, just prior to Balanced Rock, you can see that the cliffs have a sawtooth- or zig-zag-appearance. This is because the cliffs have been eroded along two sets of intersecting fractures.
13. Balanced Rock
When you get to Balanced Rock sit down and take a break, like these students from Montgomery County. Balanced Rock is a natural rock formation. The feature occurs in a block of the cliff that separated from the saw-toothed cliff wall in the ridge, up slope. The block is formed of layered sandstone. One of the layers in the upper third of the block is more easily weathered than the rest of the layers. The layer has crumbled away faster than the surrounding rock, so that it looks like the upper rock is balancing on the lower rock.
Along the trail, from Balance Rock to the cave, there are many boulders; evidence of the erosion and weathering that has formed the cliffs upslope. Erosion occurs year round along the ridge slopes, but many of these blocks were eroded hundreds of years ago, as evidenced by the trees and vegetation that often crowns them.
15 Rock shelter and cave
Between the stairs, just uphill from the cave on the Balanced Rock Trail, and the rock shelter that houses the cave, the bedrock changes from sandstones to limestones. The rock shelter and cave entrance are a great place to cool off after hiking on a hot summer day, as these students from Montgomery County are doing. The cave at the back of the shelter is in the mid-fifties (Fahrenheit) year round, and cool air blows out of the cave into the shelter during summer months.
This is one of the few limestone rock shelters in the park. Most of the rock shelters are weathered into sandstone. Here, slightly acidic waters have helped to create the rock shelter in limestone. Ground water appears to have more easily traveled through the coarser grained Ste. Genevieve Limestone, than the underlying St. Louis Limestone, resulting in the cave passage along the contact. Both units are part of the Slade Formation, a widespread Mississippian-age (~ 350 million years old) rock unit in eastern Kentucky.
The cave occurs near the boundary (contact) between crossbedded limestones of the Ste. Genevieve Limestone and the underlying finer grained limestones of the St. Louis Limestone (in the floor). You can see water dripping from the ceiling of the shelter, evidence that the shelter is still slowly forming. Look on the ceiling of the shelter for water droplets. Often these are orange-colored because they contain iron. Small orange circles on the ceiling and walls are precipitate iron, that was once carried in the ground water.
The cave can be entered from the back of the rock shelter, however, there are no lights in the cave, and sunlight only travels a short distance into the cave from the mouth. Beyond that point it is completely dark. DO NOT TRAVEL INTO THE CAVE ALONE OR WITHOUT A FLASHLIGHT. CAVES CAN BE DANGEROUS. The floor of the cave is wet, slippery, and uneven. There are a few small holes in the cave floor. Also, the ceiling is low in several parts of the cave so that it is easy to hit your head. Be careful if you choose to walk through the cave. The cave passage connects to the shaft entrance along the Original Trail to Natural Bridge and many people enjoy climbing through the cave to the other trail. However, the passage can be clogged with silt and mud. You should check with the park naturalist before your hike if you have any questions or want to be instructed on cave safety. This is not a formation cave. There are no stalactites or stalagmites, and little to see, except dark limestone walls.
Just above the lip of the rock shelter, there is a gap between two limestone beds. The underlying bed is pock-marked or mottled. This is called a caliche. It represents an ancient soil horizon, called a paleosol. The surrounding limestones were deposited in shallow seas. Evidence for a marine origin includes coral fossils in the underlying limestone. However, the caliche indicates that for at least a brief time the underlying marine deposits were exposed to the air. This may have occurred because of a fall in sea level, or the build-up of a shoal in shallow water, much like the carbonate shoals and islands of the Bahamas today.
The unit of limestone in which the cave occurs is the Ste. Genevieve limestone. It contains broad crossbeds and scours into the underlying St. Louis limestone. If you look closely you can see orange chert clasts near the base of each crossbed. The crossbeds in these limestones are slightly different than the crossbeds in the sandstones at the top of the ridge. Whereas the crossbeds in the sandstones were deposited as bars in large rivers, these limestone crossbeds were deposited as bars or sand waves in tidal channels within the ancient Mississippian seas that once covered much of Kentucky. Similar crossbeds can be seen in tidal channels in the Bahamas and other shallow marine seas today.
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