- The Hagerman Horse Quarry
Hagerman Fossil Beds National Monumentis located west of Hagerman, Idahoat the geographic division of the Snake RiverPlain. 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 the genus" Equus" in North America.
Historically, the Hagerman Horse Quarry was divided into three informal subquarries, the red, the green and white quarry
sandstones. Fossils are found throughout the monument; however the Horse Quarry continues to be the focus of paleontological research.
Hagerman Fossil Beds National Monumentvisitor center is administered by the National Park Service. There is a skeleton reconstruction of a Hagerman Horseat the visitor center in Hagerman, 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.
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 the Smithsonian Institution. The Smithsonian Institution field crew excavated from all three quarry beds during the years 1929-1931 and 1934 (Richmond and others, 2002).
University of Utah, under the direction of Mr. Golden York, acquired fossils from the quarry in 1953. The Natural History Museum of Los Angeles Countymanaged 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 the Hagerman Fossil Beds National Monumentin 1988 (Richmond and others, 2002).
Based on the documented number of skulls collected from the Hagerman Horse Quarry, at least 200
Hagerman horses are represented from the quarry. Besides the fossil horse, " Equussimplicidens", other large vertebrates collected from the quarry include an antelope, a camel and a peccary. Small mammalian fossil vertebrate generainclude hare, weasel, gopher, vole and shrew. Also represented are fossil woodland birds, waterfowl, snakes, turtles, lizards, frogs, toads, salamanders and a variety of fish. Fossil bivalvesand gastropodsare also represented from the quarry (Richmond and others, 2002).
Snake RiverPlain is comprised of riftbasin sedimentsthat accumulated during the Miocenethrough Pleistocene Epochs. These clastic sedimentarypackages, interbedded with basaltic flows, pyroclastic tephraand silicic volcanic ashes, 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). The PlioceneGlenns Ferry Formation spans 5.0 to 1.5 Ma. The formationoverlies the Branbury Basaltin the Hagerman, Idahoarea. The Glenns Ferry Formation is composed primarily of poorly consolidated lacustrineand fluvial sediments. The primary exposures of lacustrine sedimentsconsist of laterally continuous very fine-grained sandstoneand mudstonebeds that outcrop near Glenns Ferry, Idaho (47 km west of Hagerman, Idaho) (Richmond and others, 2002).
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 of sandstones, siltstones, mudstones, and shales. Basaltic flows and deposits of basaltic tephraand ashof varying thicknesses are interbedded within the sedimentary strata. Thin silicic ashbeds are also present. The formation is divided into three informal members based upon depositional facieschanges. The lower and middle members are delineated by the Peter’s Gulch rhyoliticash (age 3.7 Ma). The middle and upper members are separated by the Fossil Gulch daciteash (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, pebble sands and cobble gravel. Sedimentological data of the Tuana Gravel indicates the gravelbeds were deposited on a northwest sloping alluvialplain. Thickness of the gravel beds varies, but is about 50 feet in Fossil Gulch area. The Tuana Gravel is overlain by a caliche, thought to have formed during a Pleistocene interglacialperiod, and several feet of recent soils (Richmond and others 2002).
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 the bogmay 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 their carcasses. They concluded that depositionand burialof the carcasses occurred during subsequent flooding 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 single catastrophic floodevent.
The Hagerman Horse Quarry consists of three different
fluvial sandstones. 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 by alluvium(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. The grain sizeindicates moderate paleoflow velocitieswith a paleocurrent direction to the south-southwest. All three quarry sandstones are interpreted to be ephemeralbraided fluvial channel systems that were deposited in the Snake River Plain graben(Richmond and others, 2002).
The white sandstone accumulation, consisting of hundreds of bones, resulted from a moderate
droughtand an ephemeralflood. The Phase II drought on the Snake RiverPlain resulted in a mass mortalityof "Equus simplicidens" in addition to many other macro- and microvertebrates in the quarry area. The terrestrial animals were attracted to a drying pond or marsh, where they died of drought-induced starvation, dehydration, and illness. Decompositionprocesses 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 dry paludaldeposit, 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
stratigraphically 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. The taphonomicevidence of this bed indicates that a mass mortalityof "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).
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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