Timothy H. Heaton
Museum of Comparative Zoology, Harvard University, Cambridge, MA 02138
Porcupine Cave is located at an elevation of 2800 m in a steep glacier-cut valley in the western Uinta Mountains of Utah. The cave was discovered in 1960 by Dale J. Green and John F. Haman of the National Speleological Society who cleared rubble from a tight 12 m long horizontal crawlway to gain entry. Beyond this crawlway a larger dirt-filled passage called the Bridge Junction (2 m wide and 2 m high) slopes downward into the deeper parts of the cave. In this passage, 25 m inside the cave, Green and Haman collected a juvenile maxilla and adult cranium of black bear (Ursus americanus; UUMZ 22360-22361) and found what appear to be bear claw marks on the cave walls. The dirt fill ends 30 m inside the cave, and the passage beyond is littered with earthquake-shattered speleothems. This passage is horizontal and leads to a large room (10 m wide and 14 m high) full of breakdown blocks. In this room Green and Haman found a pair of sub-adult grizzly bear dentaries (U. arctos; UUMZ 22362) 65 m inside the cave, and the room was named the Bear's Den. These bones were donated to the University of Utah Museum of Zoology and identified by Stephen D. Durrant. The cave was mapped and described in a private publication (Haman 1963).
In 1986 I collected additional material at the Bridge Junction. The soil there, which came in from the cave entrance, is composed of fist-sized angular limestone cobbles in a clay and organic matrix partly covered with decaying sticks, roots, and bones. This soil slopes 20° and appears to be disturbed from slumping. The room was carefully mapped, and bone (now at Brigham Young University) was collected from the upper 0.2 m of soil. The rest of the juvenile black bear skull was recovered, as was about half of its skeleton (BYUVP 9960). Bones of this animal were disarticulated and widely scattered. At least two adult black bears were represented by two left maxillae, an upper canine, thoracic vertebra, metacarpal, calcaneum, and claw (BYUVP 9961-9967).
In addition to bears, a suite of boreal mammals and birds typical of the Uinta Mountains was found. The 43 bird bones (BYUVP 9855-9897) have not been identified. Of small mammals I recovered 2 jaws of snowshoe rabbit (Lepus americanus), 24 of marmot (Marmota flaviventris), 16 of northern pocket gopher (Thomomys talpoides), 3 of bushy-tailed wood rat (Neotoma cinerea), 7 of porcupine (Erethizon dorsatum), 2 of pine marten (Martes americana), 1 of long-tailed weasel (Mustela frenata), and 1 of striped skunk (Mephitis mephitis; BYUVP 9898-9959). Of artiodactyls I found 2 phalanges of wapiti (Cervus elaphus), 15 bones of mule deer (Odocoileus hemionus), and a metacarpal probably of bison (Bison bison; BYUVP 9968-9985). The bones were coated with wet clay, and some were heavily gnawed by rodents.
Several artifacts have been recovered from Porcupine Cave. Haman (1963) reported finding a white quartzite arrowhead (3 cm long and 2 cm wide) in the entrance crawlway. I found a tan chert elko series point (10 cm long and 5 cm wide) at the Bridge Junction. It was on the surface near the bottom of the soil fill; its broken tip was 1.5 m lower on the slope. Some charred, water-soaked wood was also found in the soil. A femur of the juvenile black bear was C-14 dated at 510 +/- 75 yr B.P. (GX-13292). This date suggests that this fauna (recovered near the cave entrance) and its associated artifacts are very recent.
In 1987 I collected additional bones of the grizzly bear in the Bear's Den including skull fragments and an assortment of postcranial elements. Rock fall appears to have damaged some bones and buried others. Dripping water kept these bones wet and deposited calcite on some, and some are heavily gnawed by rodents. A group of ribs was C-14 dated at 10,620 +/- 245 yr B.P. (GX-13676). This is an early date for grizzly bear, which immigrated from Asia in the late Wisconsin, but it has been found with similar dates in caves of Wyoming and Idaho (Kurtén and Anderson 1980). This grizzly bear apparently postdates the extinction of the giant short-faced bear (Arctodus simus) which is thought to have been outcompeted by the grizzly bear and which has been found in Lake Bonneville deposits of northern Utah (Kurtén and Anderson 1980; Nelson and Madsen 1983). The Porcupine Cave specimen represents the first fossil grizzly to be recovered from Utah. A few grizzly bears have been seen in the state in historic times, but now the species is extirpated (Merriam 1918; Durrant 1952). There is no evidence that humans were associated with this fossil grizzly.
The cave entrance at present is too small to admit bears, but if the fill was removed the passage would be sufficiently large. From the dated bear skeletons and their context within the cave, the following historical sequence seems likely: 1) large-scale Wisconsin glaciation eroded the valley and intersected the cave; 2) the glacier disappeared by 10,620 yr B.P. leaving the cave with a large entrance, and the grizzly bear entered the cave (possibly as a den) and died; 3) subsequent glacial activity forced debris 30 m into the cave but left the entrance open enough to admit black bears; 4) the cave was free of ice again by 510 yr B.P., and black bears (and possibly humans) entered the cave (probably as a den), leaving their remains on top of the glacial fill; and 5) subsequent glacial or other causes plugged the 15 m entrance passage with additional debris, preventing the entry of large animals.
Thanks are extended to Julia S. Heaton for helping collect and catalog the collection, Dale J. Green for providing information about the cave's discovery, Asa Nielson and Mike Hall for investigating the archaeology, the University of Utah for loaning their material, and the National Speleological Society for funding the C-14 dates.
Haman, J. F. 1963 Porcupine Cave, Summit County, Utah. Salt Lake Grotto Technical Note 61:1-9.
Kurtén, B., and E. Anderson. 1980 Pleistocene Mammals of North America. Columbia Univ. Press, New York, 442 p.
Merriam, C. H. 1918 Review of the grizzly and big brown bears of North America. U.S. Department of Agriculture, Bureau of Biological Survey, North American Fauna 41:1-136.
Nelson, M. E., and J. H. Madsen, Jr. 1983 A giant short-faced bear (Arctodus simus) from the Pleistocene of northern Utah. Transactions of the Kansas Academy of Science 86:1-9.