Nautilus Cave is located on the west side of Heceta Island about 3.5 km from the ocean and 200 m above sea level. The entrance (see photo at left) was severely damaged by clear-cut logging, and a large amount of debris fills the sink hole. A stream flows into the cave under the logs. The cave slopes downward through a crawlway and follows a sinuous stream passage for about 25 m before ending in a sump pool. Along the stream are some perched gravel deposits, apparently the result of filling of the passage with sediment followed by another cycle of erosion. The source of the sediment was probably another small sinkhole in the surface above. Several deer bones were found and recovered from these gravels by Tongass National Forest geologist Jim Baichtal. A deer humerous (see photo at right) was radiocarbon dated at 8,180 years old, making it the oldest deer bone dated from Southeast Alaska. An upper, dry passage in the cave has additional sediment from a sinkhole above. Jim Baichtal found a juvenile beaver skeleton eroding from this sediment, and it dated to 1,580 years old. This cave has not yet been visited by a paleontologist, and no sampling has been made of the sediment.
The stream in Nautilus Cave has downcut through a Silurian age limestone and has exposed some fossil mollusk shells in the bedrock (see photos below). This is a common occurrence in caves, but the fossils in Nautilus Cave are especially spectacular. The photos below are of shells exposed in the ceiling of the low stream passage. In addition to the various fossils found in Nautilus Cave, a population of cave-adapted amphipods (5 mm long) were found living in the cave. Any future excavation in this cave will have to be done with great care so as not to disturb these fragile animals.
Nautilus Cave contains fossil shells exposed in the Silurian age bedrock (408-438 million years old). At left is a coiled nautiloid (related to the living chambered nautilus) with several of its chambers visible. The cave was named after this fossil. Above is a photo of numerous gastropod (snail) shells with banded layers of stromatolite (fossil bacterial algae) above and below.