Fall Fieldwork in the Greater Yellowstone Area

Sheepeater Cliff area, Yellowstone National Park. This area is named in honor of the Shoshones who lived in this area, The name specifically comes from their use the big horn sheep – hence the name “sheepeater”. Note the columnar basalt in the cliff area which has an age of about 0.5 million years.

Doing geology field work in the greater Yellowstone area during the fall is always an adventure. This is the time that animals and birds are on the move, so it’s a good opportunity to have interesting chance encounters. In my quest to understand the Eocene thermal springs of the Gravelly Range in southwestern Montana, I’ve spent time in the Yellowstone area hiking around thermal areas. The Artists Paint Pots, located a few miles southwest of the Norris Geyser Basin, appear to be a likely analogy for the Gravelly Range thermal strata. Of particular interest is the red staining that occurs in many meters of Gravelly Range thermal deposit strata. The red stained rocks are ubiquitous in the Red Hill and Middle Springs areas.

Red Hill in the Gravelly Range, southwestern Montana, contains many meters of red-stained, thermally generated Eocene strata.
The Middle Springs area in the Gravelly Range also contains several meters of Eocene red-stained thermally-generated rocks. It’s extremely easy to confuse these rocks with the underlying red-colored Triassic Woodside Formation strata.
Red-stained thermal deposits at Artist Paint Pots.
Blood Geyser thermal pools at Artist Paint Pots, Yellowstone National Park.

The Artist Paint Pots, especially the Blood Geyser, are well known for red-colored rocks that are produced by iron oxides precipitating out of the thermal waters and staining the surrounding rocks.

As I said earlier in this blog, doing fall field work in the greater Yellowstone area usually means exciting chance encounters with various animals and birds. Some encounters are a bit more exhilarating than others, but I did manage to photo-document some in between finishing up field work for the season:

Young grizzly loading up with food (only caraway roots and mice!) in the Tom Miner Basin, Montana.

Bull moose eating on Cottonwood trees near Ennis, Montana.

Immature bald eagle near the Jefferson River, Montana.
Redtail Hawk on irrigation pipe, near Sheridan, Montana.
Trumpeter swan family resting at – ironically, Swan Lake Flats, Yellowstone National Park.
Great Horned owl giving me the evil eye…
Sandhill cranes in-flight near the Ruby Mountains, southwestern Montana.

A High-Elevation Eocene Fossil Vertebrate Site in the Elkhorn Mountains, Southwestern Montana

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The Dog Town Mine vertebrate fossil locality is an isolated occurrence of Eocene strata found on the divide between the Toston-Townsend Valley (on the east side of the photo)  and the North Boulder Valley (on the western edge of the photo), southwestern Montana.

The Dog Town Mine Tertiary fossil vertebrate locality is nestled on private property within the southern extent of the Elkhorn Mountains, southwestern Montana. The locality is about 20 miles southwest of Townsend, Montana, where Mesozoic and Paleozoic carbonate, quartzite, and red-colored mudstone, siltstone, and sandstone rocks underlie Eocene (Chadronian) strata. These unconformable Eocene strata contain the Dog Town Mine vertebrate fossil locality.

Earl Douglass (yes, that Earl Douglass of the Dinosaur National Monument fame) first collected at the site on Friday, June 27, 1902 (based on transcriptions from Earl Douglass’ journals done by Alan Tabrum and volunteers from the Carnegie Museum of Natural History). According to his journal, Douglass met a man from Toston, Montana, on horseback and this person told him about the Dog Town Mine, which was located on the divide between the Toston/Townsend and North Boulder Valleys. Douglass was headed to the North Boulder Valley anyways, so he rode to the mine where he found invertebrate fossils (brachiopods and bryozoa) in carbonate rock which was in contact with the ore deposit. A Mr. Allen, who he dined with that evening, told him that more fossils could be found a little ways west of the mine. After dinner Douglass rode a short way west of the mine and found banks along a ravine that looked like Tertiary White River beds. Here he found  “Oreodont, Ischyromys, Palaeolagus, Titanotherium, and turtle remains” (June 28, 1902, Douglass Journal entry). This area is the present Dog Town Mine vertebrate fossil locality.

The Dog Town Mine site encompasses all of the light-colored exposures on the right side of the county road.
The Dog Town Mine locality encompasses all of the light-colored exposures on the right side of the county road seen in this photograph.

 

Tertiary strata at the Dog Town Mine are fine-grained, predominantly consisting of siltstone with minor fine-grained sandstone units. The deposits are probably of aeolian origin, originating from areal sediments rich in volcanic ash. These deposits are probably similar lithologically and in mode of origin to those Tertiary White River units found at high elevations within the Laramie Range and Medicine Bow Mountains (Evanoff, E., 1990, Early Oligocene paleovalleys in southern and central Wyoming: Evidence of high local relief on the late Eocene unconformity: Geology, v. 18, p. 443–446; Lloyd and Eberle, 2012, A late Eocene (Chadronian) mammalian fauna from the White River Formation in Kings Canyon, northern Colorado: Rocky Mountain Geology, v. 47, no. 2, p. 113–132).

Vertebrate fossils have been collected at the Dog Town Mine site for various museums since Douglass’ initial collection. The Carnegie Museum of Natural History in Pittsburgh, PA houses a collection from the site as well as the Museum of the Rockies in Bozeman, MT.