Brighter future for an old natural wonder

Deborah Painter (USA)

During the 1700s, when North American colonies were under British rule, a certain highly intelligent and educated man by the name of Thomas Jefferson heard of a remarkable natural arch in west central Virginia, to the southwest of his home in Charlottesville. He purchased hectares of land surrounding the stone arch from King George III for 20 shillings. Since he bought this land in the year 1774, it was a well-timed transaction. The King might not have dealt so amenably with Jefferson following his involvement in writing the Declaration of Independence. The future third President of the United States was immensely interested in both architecture and natural history, and showed his understanding of both in his description: “… the arch approaches the semi-elliptical form, but the larger axis of the ellipsis, which would be the cord of the arch, is many times longer than the transverse”.

Cedar Creek runs beneath the Natural Bridge of Virginia, which, in the 1800s, was named one of the seven Natural Wonders of the World. The creek flows through a gorge. Native Americans of the Monacan tribe had for many thousands of years camped beneath Virginia’s Natural Bridge during hunting expeditions and made use of Cedar Creek’s water. They also found the bridge itself useful as a crossing.

When the Commonwealth of Virginia divided its western frontier into counties, it named the county containing the natural wonder ‘Rockbridge County’. Early explorers of the 1700s were awestruck by how this towering dolostone and limestone arch resembles a bridge built by human hands. It is approximately 65.5m in height from the top of its arch to the trail below, and 27.43m from end to end. The most famous angle is seen in Fig. 1, facing north-northwest, with a less famous view facing southeast (Fig. 2.).

Europeans were generally unfamiliar with natural stone arches in the 1700s and did not know of the two thousand natural arches at what is now known as Arches National Park in Utah. In the 1800s, the Natural Bridge was further promoted by an 1835 painting by Jacob Caleb Ward. Today, the picture is displayed at the Nelson Atkins Museum in Kansas City in Missouri. The Pennsylvania Railroad used this painting as its logo for many years. Salisbury Jonroth of Great Britain manufactured a china tea cup and saucer set depicting the Natural Bridge, among other North American attractions, such as Carlsbad Caverns.

Why are there so few limestone or dolomite spans of similar nature and appearance worldwide? The answer is to be found in the karst geology of the region. The Appalachian Valley (known locally as the Shenandoah Valley) is unusually narrow in the area near Natural Bridge and the City of Lexington. The rocks of the valley are Cambrian and Ordovician in age, sedimentary rocks that were folded and thrust faulted. Karst topography characterizes the Natural Bridge area. (A karst landscape is formed by the dissolution of soluble rocks, such as limestone, dolomite and gypsum; and is characterised by underground drainage systems with sinkholes and caves.)

Near the Natural Bridge and Natural Bridge Station is Short Hill, a small hill that is a textbook example of a synclinal mountain. The Natural Bridge itself is composed of two sedimentary rock formations: massively bedded, dense light grey arenaceous dolomite (dolostone) of the Beekmantown Formation of Ordovician age; and dark blue limestones of the Chepultepec Formation, also of Ordovician age (Spencer et al, 2007). These are all marine clastics.

Cedar Creek is believed to have begun as an above ground stream less than one million years in the past. It is entrenched at its mouth at the James River near Gilmore Mills for a distance of roughly 6.4km upstream to Red Mills near the Bridge. In his 1968 paper on Rockbridge County geology, geologist Edgar W Spencer of Washington and Lee University built his hypothesis of the formation of the span upon earlier hypotheses promoted by H P Woodward in 1936 and by F J Wright in 1934. Woodward and Wright stated that the stream known today as Cedar Creek was part of the karst system of underground rivers, capturing water from Poague Run approximately 3.2km to the north, contributing to the larger drainage basin.

The creek’s larger flow helped to form the present-day gorge or small canyon, significantly increasing the distance from the bottom of the water flow to the roof of the underground channel. Extensive faulting characterises the bedrock here. Over a period of perhaps 500,000 or more years, the cave ceiling above that underground river collapsed bit by bit due to faulting, erosion and weathering, and ultimately disappeared. Spencer’s, Woodward’s and Wright’s hypothesis for the existence of the Natural Bridge is the accepted one today. As they stated, the Bridge is the sole remnant of that cave roof and still stands due to the strength afforded it as the midpoint of a syncline.

Today, the “Lost River”, about 800m upstream from the Natural Bridge, is an example of an underground stream supporting the hypothesis of the underground river. Water from the side of the gorge flows into the Cedar Creek, much as the ancestral Cedar Creek underground river allegedly flowed into Cascade Creek that flows parallel to Cedar Creek. A section of the rock between Cedar Creek and the bedrock of the gorge was blasted away so that one can hear the underground river rushing along, but out of sight (Fig. 3).

The various owners of the Bridge established a hotel, later to be named the Natural Bridge Hotel, to accommodate the many visitors who travelled to see this sight and preserved many natural heritage resources along the streambank trail leading to Lace Falls. One such resource is a cave where bat guano was harvested hundreds of years ago to make saltpetre, a component of gunpowder (Fig. 4).

This was a source of income for Thomas Jefferson from his investment. Several extremely old specimens of arbor vitae (Thuja occidentalis), also known as eastern white cedar (Fig. 5), provide shade along the steps leading from the modern visitors’ centre to the trail.

These individual trees are up to 700 years old. A dead trunk, not pictured, has been preserved in situ; the tree died in 1980 at the age of approximately 1,600 years. The arbor vitae specimens doubtless gave Cedar Creek its name. Decades ago, the owners built a concrete footpath from the top of the gorge down past the trees to the gorge, and a stone wall separates the visitors from the creek along portions of the 1.4km-long trail where the grade is steep.

Interesting features near the span along the gorge are fossil moss being formed in the open as calcite laden water flows almost constantly over it (Fig. 6), the saltpetre cave referred to above and lost river, younger specimens of arbor vitae, and riffle and pool complexes and small rapids and falls at various points along the trail (Figs. 7, 8, 9, 10 and 11), providing prime habitat for a variety of fish and invertebrates.

At the end of the trail is a 9m-tall cascade known as Lace Falls (Fig. 12).

Near US 11, approximately 760m north of the visitors’ centre and at latitude 37° 38’ 05.65” North and longitude 79 ° 32’ 37.76 West we were able to collect some loose specimens of dolomite on private land after permission was obtained from the owner (Figs. 13, 14, 15 and 16). They displayed interesting features that looked like bits of Chepultepec limestone and a number of small white markings.

Native Americans and wild game used the Bridge as a footpath to save time long before the coming of the Europeans. Then the game trail became a stage road, then a paved road for automobiles and trucks as the stage road became absorbed into a portion of the main north-south roadway corridor through the Shenandoah Valley, US Route 11. This road still uses the Bridge as an official crossing.

Yet, even with the advent of US government mandated bridge inventories and inspections beginning in the late 1960s, no formal inspection of the stone span was carried out for many decades to determine if it was suitable for sustained use in the era of large diesel trucks. The construction of Interstate 81 from New York south to Tennessee was to some degree helpful; some of the heavy traffic that once used the Bridge would now use the modern multilane highway.

One would think then that this scenic wonder would always be afforded the preservation worthy of its historic significance. Although the owners of the Natural Bridge at Cedar Creek did preserve the saltpetre cave and native vegetation, including the extremely old arbor vitae trees along the trail from the Visitors Center to Lace Falls, their ability to keep the gorge free of vandals and graffiti artists (Fig. 17) and to preserve the natural resources of the land to the north, south and west was limited.

Angelo Puglisi was the most recent private owner, having purchased the complex, including the Natural Bridge Hotel, in 1988. When he made the announcement in 2013 that he planned to sell the property, there was the possibility that it might be divided up into smaller tracts with multiple ownership and less attention devoted to preservation of its historic, scenic and natural assets. Rockbridge County and the cities of Buena Vista and Lexington passed resolutions stating that a good outcome was needed. Land trusts throughout the United States worked together.

The Rockbridge Area Conservation Council and the Valley Conservation Council formed the Friends of the Natural Bridge. A non-profit Virginia Conservation Legacy Fund was headed by Tom Clarke. Mr. Puglisi donated 76 hectares and the group paid for another 526 hectares with a loan from the Virginia Clean Water Revolving Loan Fund from the Virginia Resources Authority and the Virginia Department of Environmental Quality. Thanks to Mr. Puglisi and the Virginia Conservation Legacy Fund, the Natural Bridge and Visitors Center, as well as hundreds of hectares surrounding them, became part of the state parks system. The Natural Bridge Hotel and Conference Center remained in private ownership.

For a few decades prior to the sale of the tourist complex, public visitation had decreased. But the establishment of the Natural Bridge State Park boosted visitor use dramatically. The park rangers furnish a vehicle that drives tired visitors back to the visitor’s centre when they return to the Bridge at the end of their hike from Lace Falls. This might account for some of the increased visitor traffic, since there are four flights of timber stairs leading from the canyon back to the crest of the hill. An August 2019 trip to Natural Bridge State Park gave me many pleasant surprises after not visiting this beautiful site for a few decades.

Signage along the trail now prohibits visitors from entering the saltpetre cave to avoid disturbing roosting or hibernating bats. This prohibition is strictly enforced. Other sensitive habitat areas are marked “no trespassing”. Another addition is a recreation of a Monacan Indian village along the trail (Figs. 18, 19 and 20), which was supervised by descendants of the Native Americans, who had camped and lived in the gorge.

The State Park is located at 6477 South Lee Highway, Natural Bridge, Virginia. For more information visit their web site at: http://www.dcr.virginia.gov/state-parks/natural-bridge.

The Caverns at Natural Bridge, not a part of the State Park, is very near, at 15 Appledore Lane, Natural Bridge, Virginia, 24578, and is a very interesting karst feature in its own right.

Thanks to a partnership between the Virginia Department of Conservation and Recreation and the Virginia Department of Transportation, geologists were subcontracted in early autumn of 2017 to perform varied methods of non-destructive testing of the Bridge, including electrical resistivity, geophones (small seismic sensors) and Ground Penetrating Radar testing.

The conclusion of the testing is that fractures and internal voids have developed in the dolostone. It is inconclusive if this is the result of vehicular use, but to err on the side of caution, the Virginia Department of Transportation is studying alternative routing for this segment of US Route 11 and is writing an environmental document towards that end.

About the author

Deborah Painter is an ecologist and general environmental scientist specialising in government and industrial development planning to minimize deleterious environmental impacts. She lives in the United States.

References

Kastning, Ernst H., PhD. 2014. Images of America: Natural Bridge. Arcadia Publishing. 128 pages.

Lucas, Rachel. Channel 10 News Roanoke, Virginia April 12, 2018.  “Route 11 Over the Natural Bridge Should be Removed According to VDOT”

https://www.wsls.com/news/route-11-over-natural-bridge-should-be-moved-according-to-vdot.

Spencer, Edgar W. 1968. Geology of the Natural Bridge, Sugarloaf Mountain, Buchanan, and Arnold Valley Quadrangles, Virginia. Report of Investigations 13. Virginia Division of Mineral Resources, Department of Conservation and Economic Development.

U. S. Geological Survey. 2019. Geologic Units of Rockbridge County, Virginia.

https://mrdata.usgs.gov/geology/state/fips-unit.php?code=f51163.

U. S. Department of Agriculture Plants Profile for Thuja occidentalis.

https://plants.usda.gov/core/profile?symbol=THOC2.

Virginia Department of Transportation. Studies: Rockbridge County Natural Bridge State Park https://www.virginiadot.org/projects/staunton/rockbridge_county_8211_route_11_natural_bridge_state_park.asp.

Wilkes, Gerald P., Edgar W. Spencer, Nick H. Evans and Elizabeth V. M. Campbell. 2007. Geology of Rockbridge County, Virginia. Commonwealth of Virginia Department of Mines, Minerals and Energy. Virginia Division of Mineral Resources Publication 170.

Woodward, H. P., 1936a. Geology and Mineral Resources of the Natural Bridge region. Virginia: Open-file report, Virginia Division of Mineral Resources.

Wright, F. J. 1934. The newer Appalachians of the south. Denison University Bulletin, volume 34, p. 1-105.