El Capitan Cave

El Capitan Cave is the largest known cave in Alaska, and is also the first cave in Southeast Alaska where fossil bones were discovered. The cave entrance faces south across the shallow El Capitan Passage, providing a nice view of Kosciusko Island (photo at left). It is also located above the El Capitan Forest Service Camp, which gets its water from a spring that emerges below the cave (and ultimately from a river inside the cave). A wooden stairway has been constructed up the long hillside to the cave (see photo below), and tours are provided for visitors by Tongass National Forest. A gate has been installed in the cave to prevent visitors from falling into pits or being trapped behind a portion of the cave that floods during storms.

In 1990 while exploring a remote upper passage of El Capitan Cave, caver Kevin Allred discovered a passage filled with exposed bear bones. He named it the Hibernaculum. The bones appeared to be close to a former second entrance to the cave that had become sealed. Paleontologists Tim Heaton and Fred Grady were notified and made separate trips to the site with Allred in 1991. Both agreed that an excavation would be too difficult using the torturous route that Allred had used, so the sealed entrance had to be located and exhumed. A search of the mountainside produced no sign of the sealed entrance. So the cave map was used in conjunction with a compass, tape, and programmable calculator to locate the point directly above the bear den, and the hole was found by yelling to Allred who was inside. The spot was flagged, and in 1992 the sealed entrance was opened and the excavation was accomplished by in a two-week period. Heaton and Grady were assisted by cavers and Forest Service archaeologists. The excavation was funded by the National Geographic Society and Tongass National Forest. Following the excavation, the Hibernaculum entrance was securely sealed again.

Dr. Heaton points to the sealed Hibernaculum entrance of El Capitan Cave (left), and Dan Monteith negotiates the crawlway below (right).

The most prominent fossil in the cave was the skeleton of a large female black bear (Ursus americanus) in the widest part of the passage, 20 meters inside the sealed entrance in the lower part of the den (see photo at right). This was a rocky area with shallow sediment, and the skeleton was exposed and showed no sign of having been buried. The bones were wet and deep red in color. The preservation was exquisite, and virtually every bone of the skeleton was represented. Some of the the toe bones were even laid out in their anatomical positions (see photos below). The skeleton was contained within a small area and showed no signs of scavenging. This led some of the cavers to think that the skeleton was very young. But the paleontologists noticed that even though the bear appeared to be a gracile female, it seemed too very large for a modern black bear. Black bears were considerably larger during the Late Pleistocene epoch. Sure enough, when radiocarbon dated this skeleton turned out to be 10,750 years old.

Many of the bones of this black bear were found in the sediment in their anatomical positions.

Closer to the sealed entrance, parts of several other black bear skeletons were found scattered about in an area of deeper, more organic sediment. This included skulls or partial skulls that were radiocarbon dated to 11,565, 11,540, and 6,415 years old. These dates demonstrated that black bears had been living on Prince of Wales Island since early postglacial times. Many other black bear bones were recovered in this area, but it was difficult to determine which of the skulls (if any) they were associated with.

Another thing that caught the attention of the cavers and paleontologists when they first entered the Hibernaculum was the presence of some giant bear bones. They were so large that there was speculation that they might belong to the giant short-faced bear (Arctodus simus). But on closer examination they turned out to belong to an enormous individual of brown bear (Ursus arctos). Fragments of this giant were found scattered along the crawlway near the sealed entrance, and they were radiocarbon dated to 9,760 years old. Parts of a smaller brown bear were found scattered about in the lower den near the complete black bear skeleton. Nearly every bone found had bite and puncture marks made by another bear. This individual dated to 12,295 years--the oldest from the cave (see photos below).

Parts of a very large brown bear were found scattered and buried in the upper portion of the den (left). The oldest dated fossil from El Capitan Cave is a smaller brown bear, whose parts were found scattered throughout the lower den (right). Nearly every element of this bear has bite marks made by another bear.

Brown bears do not live on Prince of Wales Island or any of the coastal islands south of Frederick Sound today, but they are the only bears living on the islands north of Frederick Sound. This peculiar distribution pattern had led biologist David Klein to propose that as brown bears moved southward from Alaska and black bears moved northward from the lower states following deglaciation, the first species of bear to colonize any island was able to exclude the other. But contrary to this hypothesis, the fossils of El Capitan Cave demonstrated that both species coexisted for a long period of time.

This red fox jaw and an upper canine were found in El Capitan Cave and, like brown bear, represent a species no longer living on Prince of Wales Island (left). Juvenile otter bones are found associated with fish bones from otter scat, showing that otters were denning in this cave passage before it became sealed (right).

In addition to brown bears, two other carnivores not living on Prince of Wales Island were found in the cave. A red fox (Vulpes vulpes) jaw was dated to 10,050 years old (see photo above). A tooth fragment matching wolverine (Gulo gulo) was also found. These discoveries were unexpected and seemed inconsistent with the notion that mammals slowly colonized barren islands following the Ice Age. All other species found in El Capitan Cave still live on the island. Bones of juvenile river otters (Lontra canadensis) were found along with large volumes of fish bone and invertebrate fragments from otter scat (see photo above). The most abundant micromammal was long-tailed vole (Microtus longicaudus), and others found were deer mouse (Peromyscus), ermine (Mustela erminea), shrew (Sorex), and bat (Myotis). Song bird bones and land snail shells were also found.

Paul Matheus uses a rake to search for bones in a pool at the end of the Hibernaculum passage (left). A Forest Service trailer is turned into a makeshift laboratory where bones are dried and sediments are screened and searched for small bones and teeth (right).

Bones exposed in El Capitan Cave were photographed in place and mapped according to a grid system. Then they were removed and were cleaned, dried, and cataloged in a makeshift lab at the El Capitan Forest Service Camp. Sediments were sampled and wet screened in camp (154 gallon-size bags in all). This allowed for recovery of small mammal, bird, and fish bones. In some areas of the cave layers of different types of sediment were found, but nearly all the fossils were found in the upper, more organic sediments.

El Capitan Cave opened the door to elucidating the Ice Age prehistory of Southeast Alaska, and the discoveries received wide media attention. This made members of the Tongass Cave Project and Forest Service scientists more aware of the fossil potential in Alaska's caves. And even as the El Capitan excavation was underway, other caves with late Pleistocene bones were located on Prince of Wales Island.

   
© 2002 by Timothy H. Heaton