Valley Forge’s Cave of Bone

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I am a transplant from the Midwest and am Cleveland born and bred.  One of my favorite pastimes there was the exploration of historical sites and personal narratives.  I have lived in the Philadelphia area for 11 years and still marvel at how lucky I am to live here.  It’s such a unique area with its history, food, and people.  One of my favorite aspects of living in this area is learning about the historical sites that abound.  I have often said that it is difficult to throw a stone with hitting something of historical value (or a pizza shop).

After researching the Kennedy-Supplee mansion, I began to do a look through the website and found more interesting locations to explore. One of the locations is called the Port Kennedy Bone Cave. It’s a limestone cave in the Port Kennedy section of Valley Forge Park and contains prehistoric fossils. The fossil deposit is from the Irvingtonian period and was caused when plants, insects, and animals fell into a sinkhole.  It’s considered to be one of the most significant Pleistocene Epoch fossil deposits in North America.  The site was found in the 1870s during routine limestone mining.  After the initial expedition the site was covered.  Another expedition began in 1893 after subsequent mining at a lower level exposed more of the site.

The expeditions by Mercer, Wheatley and Cope and Mercer and Dixon identified 1200 fossils including a “giant ground sloth, mastodon, tapir, peccary, skunk, short-faced bear, saber-toothed cat, and many other taxa” (NPS History).   The original studies found “Most of the seeds represent hickory, beech, pine, and creeper. Most of the leaves belong to willow. Sphagnum moss was also found. Hickory also made up most of the identifiable wood, and oak was also present. A dozen species of beetles were found, but no other invertebrates were reported, or any fish. Amphibians and reptiles are represented by frogs, turtles, and snakes. The only bird appears to be a turkey. Many kinds of mammals were found, including: ground sloths, shrews, rodents, rabbits, pikas, bats, mustelids (including badgers, martens, otters, and wolverines), skunks, several varieties of felines (including bobcats, American cheetahs, and saber-toothed cats), dogs, foxes, short-faced bears, black bears, mastodons, horses, tapirs, deer, and peccaries.” (

Mining of the cave stopped in 1896 due to groundwater which flooded the area and made it impossible to mine.  The location of the cave became obscured when the Ehret Magnesium Manufacturing Company filled the cavity with manufacturing waste containing asbestos. Over time the site became covered by vegetation. The site went untouched and missing until Valley Forge Park commissioned a group to find the cave.  A study based on field notes from the original expedition was done in 2005.  Edward B. Daeschler,  assistant curator in the Department of Vertebrate Zoology from the Academy of Natural Sciences,  Matthew C. Lamanna, assistant curator in the Section of Vertebrate Paleontology from the Carnegie Museum of Natural History, and Margaret A. Carfioli, biological science technician from the Valley Forge National Historical Park found the missing site in a quarry.  The site is still originally preserved with the asbestos material still covering it.

The area is still providing more clues to its prehistoric past.  I recall reading an article in 2019 about a dinosaur fossil found in the park which is being kept secret so as to preserve the fossil from theft or alteration. The fossil was found on a trail by a volunteer who has a background in paleontology and geology.  The rock is 210 million years old argillite and the fossils are from the Triassic period.  The fossil appears to be three-toed impression of a dinosaur and an impression of a modern crocodile.  The fossil impressions are not considered rare or unique but are still protected through its undisclosed location.



NPS History:

Dinosaur tracks make fresh impression at Valley Forge park

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