D.C.'s Underground Bald Cypress Fossils

The area around 17th and M Streets in Northwest Washington, DC marks the northern edge of an ancient swamp, where stands of enormous bald cypress trees once lived to be 1,700 years old. Just twenty feet under the busy streets of Washington D.C., fossilized stumps of these majestic trees have been buried for millennia.

In 1922, crews excavating for construction of the Mayflower Hotel one block west on Connecticut Avenue uncovered the fossils of bald cypress stumps eight feet in diameter. The construction of other large buildings on nearby 17th Street – the Operating Engineers Building in 1955 and National Geographic’s 1961 addition – turned up similar fossils. The bases of these trees are believed to have been buried during the late Pleistocene epoch (126,000 to 9700 BCE) when melting glaciers deposited tons of silt and gravel at their roots, shifting the terrain and the flow of tidal waters from the Potomac River. The bald cypress is a close relative of the California redwood, and because they are among the longest-lived plants in North America their fossilized tree rings are tremendously valuable for scientists interested in the effects of climate change. The overlapping records of their thousand-year lifespans can be compared with those found along the east coast as far south as Guatemala, helping to create a detailed understanding of climate over many millennia. 

You can still see bald cypress trees in this part of town – the very same species as the fossilized ones – planted just north of the While House in Lafayette Square. There are four of them dating to the mid-19th century, but without the mucky water around their roots they are missing the curious “knees” that are a characteristic of their natural swampy habitat. Washington is still called a swamp by some, and with such long lifespans these too may one day be rediscovered as part of our epoch’s fossil record, this time mixed with the stones of the capitol buildings. 

We’ll have to come back in 100,000 years to find out.