- The Hagerman Horse Quarry
The
Hagerman Fossil Beds National Monument is located west ofHagerman, Idaho at the geographic division of theSnake River Plain. The Hagerman Horse Quarry is an integral part of the monument and is located on the northern flank of Fossil Gulch in the northern portion of the monument.The Hagerman Horse Quarry resides near the top of the hillside of Smithsonian Hill. The hill was named from the early Smithsonian excavations of the
Hagerman horse ("Equus simplicidens"). The Hagerman Horse is the first fossil representation of thegenus "Equus " in North America.Historically, the Hagerman Horse Quarry was divided into three informal subquarries, the red, the green and white quarry
sandstone s. Fossils are found throughout the monument; however the Horse Quarry continues to be the focus of paleontological research.The
Hagerman Fossil Beds National Monument visitor center is administered by theNational Park Service . There is a skeleton reconstruction of aHagerman Horse at the visitor center inHagerman, Idaho . The Hagerman Fossil Beds National Monument reopened the Hagerman Horse Quarry during the summer of 1997. The Hagerman Horse Quarry is closed to visitors.History
The Hagerman Horse Quarry has experienced a diverse collection history. Elmer Cook, a local rancher and resident of the area, first discovered fossil horse remains in the late 1920’s. He reported the find to Dr. Harold T. Stearns of the
United States Geological Survey , who in turn brought it to the attention of Dr. James W. Gidley of theSmithsonian Institution . The Smithsonian Institution field crew excavated from all three quarry beds during the years 1929-1931 and 1934 (Richmond and others, 2002).The
University of Utah , under the direction of Mr. Golden York, acquired fossils from the quarry in 1953. TheNatural History Museum of Los Angeles County managed their excavation during the summer of 1966. The Idaho Museum of Natural History collected material during the fall of 1966 and early summer of 1967. The following year, the Pacific Union College of Northern California conducted a small excavation. An unknown quantity of fossil material was removed prior to the establishment of theHagerman Fossil Beds National Monument in 1988 (Richmond and others, 2002).Quarry Fossils
Based on the documented number of skulls collected from the Hagerman Horse Quarry, at least 200
Hagerman horse s are represented from the quarry. Besides the fossil horse, "Equus simplicidens", other large vertebrates collected from the quarry include an antelope, a camel and apeccary . Small mammalian fossil vertebrategenera include hare, weasel, gopher, vole and shrew. Also represented are fossil woodland birds, waterfowl, snakes, turtles, lizards, frogs, toads, salamanders and a variety of fish. Fossilbivalves andgastropods are also represented from the quarry (Richmond and others, 2002).Quarry Stratigraphy
The western
Snake River Plain is comprised ofrift basinsediments that accumulated during theMiocene throughPleistocene Epoch s. These clasticsedimentary packages, interbedded withbasalt ic flows,pyroclastic tephra andsilicic volcanic ash es, have a cumulative thickness of 1524 meters (5000 feet), span about 10.5 Ma, and comprise the seven formations of the Idaho Group (Fig. 2). The seven formations, in ascending order, are the Poison Creek, Branbury Basalt, Chalk Hills, Glenns Ferry, Tuana Gravel, Bruneau and Black Mesa Gravel (Richmond and others, 2002). ThePliocene Glenns Ferry Formation spans 5.0 to 1.5 Ma. Theformation overlies the BranburyBasalt in theHagerman, Idaho area. The Glenns Ferry Formation is composed primarily of poorly consolidatedlacustrine andfluvial sediments . The primary exposures oflacustrine sediments consist of laterally continuous very fine-grainedsandstone andmudstone beds that outcrop near Glenns Ferry, Idaho (47 km west ofHagerman, Idaho ) (Richmond and others, 2002).In the
Hagerman Fossil Beds National Monument , the Glenns Ferry Formation has a maximum thickness of approximately 183 meters (600 feet) and spans the interval 4.5 to 3.0 Ma. The Glenns Ferry Formation consists ofsandstones ,siltstones ,mudstones , andshales .Basalt ic flows and deposits of basaltictephra andash of varying thicknesses are interbedded within thesedimentary strata . Thinsilicic ash beds are also present. The formation is divided into three informal members based upondeposition alfacies changes. The lower and middle members are delineated by the Peter’s Gulchrhyolitic ash (age 3.7 Ma). The middle and upper members are separated by the Fossil Gulchdacite ash (age 3.3 Ma) (Richmond and others, 2002).Lithostratigraphically, the Hagerman Horse Quarry is located within the upper member of the Glenns Ferry Formation and lies 9.5 meters below the contact with the overlying Tuana Gravel. The Plio-Pleistocene Tuana Gravel unconformably overlies the Glenns Ferry Formation and is described as a series of cyclic beds of
silt , pebblesand s and cobblegravel . Sedimentological data of the Tuana Gravel indicates thegravel beds were deposited on a northwest slopingalluvial plain. Thickness of the gravel beds varies, but is about 50 feet in Fossil Gulch area. The Tuana Gravel is overlain by acaliche , thought to have formed during aPleistocene interglacial period, and several feet of recentsoil s (Richmond and others 2002).Quarry Deposition
Dr. James W. Gidley (1930) originally interpreted the Smithsonian fossiliferous red sandstone bed to have been deposited in a bog or water hole. Death of the animals, he thought, was the result of
attrition . C. L. Gazin (1934) agreed with Gidley’s depositional interpretation, but suggested thebog may have trapped the animals. Basing their conclusions on historical information, photographs, and collection samples, Akersten and Thompson (1992) proposed the fossil accumulation was the result of a single flood event, which trapped and killed the horses, then transported theircarcass es. They concluded thatdeposition andburial of the carcasses occurred during subsequentflood ing events. Basing his interpretation on historical information and photographs coupled with a population configuration of ancient horse herds, G. McDonald (1996) suggested the horses were killed in a singlecatastrophic flood event.The Hagerman Horse Quarry consists of three different
fluvial sandstone s. The Smithsonian Institution field crew excavated from all three quarry beds during the years 1929-1931 and 1934. The three sandstone beds are informally called the red, green, and white sandstone beds (Gazin, 1934). The Hagerman Fossil Beds National Monument reopened the Horse Quarry during the summer of 1997. The only sandstone now exposed within the monument is the white sandstone. The red and green sandstone remain covered byalluvium (Richmond and others, 2002).The white sandstone is a medium grained, poorly sorted, trough cross-bedded braided
fluvial channel . Presently there is a longitudinal channel bar remaining in the quarry. Thegrain size indicates moderate paleoflowvelocities with a paleocurrent direction to the south-southwest. All three quarry sandstones are interpreted to beephemeral braided fluvial channel systems that were deposited in the Snake River Plaingraben (Richmond and others, 2002).Taphonomy
The white sandstone accumulation, consisting of hundreds of bones, resulted from a moderate
drought and anephemeral flood. The Phase II drought on theSnake River Plain resulted in a massmortality of "Equus simplicidens" in addition to many other macro- and microvertebrates in the quarry area. Theterrestrial animal s were attracted to a drying pond or marsh, where they died of drought-inducedstarvation ,dehydration , and illness.Decomposition processes resulted in a substantial accumulation of disarticulated bones (i.e. bones of skeletons that are no longer joined together). Subsequently, an [ephemeral] flood traversed the drypaludal deposit, transporting and depositing the bones. Geologic and taphonomic evidence indicates the bones traveled a very short distance prior to deposition and burial (Richmond and others, 2002).The red sandstone bed, which
stratigraphic ally underlies the white sandstone bed, also contains fossil material. The Smithsonian Institution excavated the majority of the Hagerman horse fossils from this bed during the 1930’s. Thetaphonomic evidence of this bed indicates that a massmortality of "Equus simplicidens" was the result of an earlier drought. The red sandstone bed was deposited under fluvial conditions similar to those evidenced in the white sandstone bed (Richmond and others, 2002).References
Richmond, D.R., McDonald, H.G., and Bertog, J., 2002, Stratigraphy, sedimentology and taphonomy of the Hagerman Horse Quarry, Hagerman Fossil Beds National Monument, Hagerman, Idaho, 100 p.
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