Saturday, March 14, 2015

Tule Springs Fossil Beds National Monument

I'm sorry about the gap there. I was traveling for work in the Southwest, and was unable to take the time to write anything. Here, though, is a piece about one of the places I saw, albeit briefly: one of the newest National Monuments, Tule Springs Fossil Beds National Monument. This site, north of Las Vegas, was declared in December 2014. It is noted for its abundant Pleistocene fossils, the depth of knowledge concerning its geologic and climatologic history, and historically notable investigations. Having just been established, there are no official National Park Service facilities quite yet.

Looking out across part of the southern end of the monument, facing north-northeast.


History

The reason so much is known about the Pleistocene paleontology and geology of the Tule Springs/Upper Las Vegas Wash area goes back to serendipity and archeology, a bit like how dinosaurs were found in Mongolia, but with fewer velociraptors. If you've got Springer et al. (2011), you'll find most of the below in greater detail, but we're here and that's there, so let's push on.

A geologist named Josiah Spurr appears to have made the first scientific report of fossils from this area, consisting of "mastodon" bones (more likely mammoth; if we had the teeth, we'd know in an instant, but for the record mastodons don't seem to have liked the area) from between Corn Creek Springs and Tule Springs (Spurr 1903). A second isolated occurrence comes our way via Chester Stock and Richard J. Russell of the University of California Museum of Paleontology, who collected a few more odds and ends in 1919. A promising but brief false start occurred in the 1930s. Fenley Hunter and A. C. Silberling found an obsidian flake and charcoal among vertebrate fossils in 1933 (Simpson 1933), which drew Mark Harrington of the Southwest Museum. This was just a few years after the first good examples of evidence of prehistoric humans interacting with extinct Pleistocene animals, such as the site on which the Folsom and Clovis cultures were described. Harrington was understandably interested in finding more evidence, but the Upper Las Vegas Wash was playing coy. About the best he could come up with were some bones he interpreted as butchered (Harrington 1934).

With the postwar discovery of the radiocarbon dating technique, some of Harrington's charcoal went in for dating, and proved beyond the capabilities of the technique at that time (greater than 23,800 radiocarbon years old). Thus fortified, he returned to the wash for further exploration, bringing us up to the end of the 1950s. At this time, Willard Libby, one of the founders of the radiocarbon technique, was moving to a new laboratory at UCLA and was searching for an ambitious archeological project to test his new facilities. After deliberation, Tule Springs was chosen for its potential to show associations between prehistoric humans and Pleistocene mammals. The University of California system, Nevada State Museum, Southwest Museum, and others joined forces for a massive multidisciplinary investigation called the Tule Springs Expedition, which took place in the winter of  1962–1963. They didn't go in for half-measures, either: an area just shy of a square mile (about 2.4 square km) was chosen, with a subset 700 ft by 2,200 ft (210 m by 670 m) selected for more detailed investigation, and ten 15-ft (4.6 m)-deep trenches prepared. A radiocarbon technician visited three days a week and brought samples back to UCLA, returning with the dates the next week, for a total of more than 80 dates. The geology, vertebrate and invertebrate paleontology, and fossil pollen were carefully documented, giving an outstanding picture of the late Quaternary history of the area. Unfortunately for archeology, very few artifacts were found, and they were all stratigraphically above the fossils of extinct mammals. The results are documented in a thick monograph edited by Wormington and Ellis (1967).

An areal view of the study area with its trenches, from Haynes (1967).
It's a bit hard to grasp the scale from the previous photo. Here we are at one of the trenches, as shown in Haynes (1967). Note the truck on the left.

A funny thing happened after the excitement of mass archeology faded: the area kept turning out fossil bones. During the 1990s, workers from the San Bernardino County Museum began salvage paleontology in the wash as the Las Vegas metro grew northward. They were finding tens of thousands of bones from previously unknown sites, which is not something you come across every day, and received permission from the Nevada BLM to make a more detailed paleontological survey. While making this survey, in 2003–2004, they found 438 new fossil localities. A number of interests came together to call for protection of the area. A national monument was proposed in 2010, and Tule Springs Fossil Beds National Monument was signed into law in December 2014.

Geology

The Tule Springs area does not have any bedrock exposures, instead being covered by more than 100 ft (30 m) of Pleistocene and Holocene sediments (Bell et al. 1998; Ramelli et al. 2011). The fossiliferous deposits are sometimes known as the Las Vegas Formation, after Longwell et al. (1965), who interpreted the sediments as lake deposits. These deposits are now known to have been formed by groundwater discharge (Quade 1986). They are primarily composed of silt and finer particles, making them notably finer-grained than other types of deposits in the area (Bell et al. 1998). Haynes (1967) divided the fossiliferous beds into seven major units, some with subunits, designated in ascending order from A to G. A and B are too old for radiocarbon dating, so thermoluminescence has been used. Approximate ages are as follows (A-E after Ramelli et al. 2011, F and G after Mehringer 1967):
A: 225,000 to 131,000 years
B: 144,000 to 89,000 years
C: 36,000 to 24,000 years
D: 30,000 to 18,000 years
E: 17,300 to 7,000 years
F: 5,000 to 1,000 years
G: about 1,000 years to the present

Most of the fossils come from units, B, D, and E, but there are also a few fossils in C (Springer et al. 2010). The deposits reflect a mosaic of settings, including flowing springs, meadows, streams, and wetlands (Austin et al. 2005). Pollen indicates shifting between sagebrush-dominated desert and moister, perhaps cooler conditions during deposition of the B and D units, and a juniper-sagebrush woodland on the valley floor during deposition of Unit E (Mehringer 1967).

Paleontology

Although Tule Springs is most famous for vertebrates, its fossils include a variety of other organisms as well. Plants are represented by algae, woody fragments, and pollen of Ephedra, conifers, and angiosperms (Mehringer 1967), and wood, charcoal, and other plant remains are found throughout (Bell et al. 1998). Invertebrates are represented by abundant clams and snails (Taylor 1967), and cicada burrows (Bell et al. 1998). The vertebrates can be divided into three assemblages, from the B2, D, and E1 units. The oldest assemblage, from the B2 unit, includes waterfowl (scaups and coots), the extinct condor-like bird Teratornis, the sloths Megalonyx and Nothrotheriops, a vole, rabbits, a small felid, the “American lion” Panthera atrox, Columbian mammoths, at least two species of horses, the camel Camelops hesternus, and bison. The D unit assemblage includes Columbian mammoths and Camelops. The most recent assemblage, from E1, includes waterfowl (coots, scaups, and widgeons), owls, hawks, a sloth, several species of rodents and rabbits, coyotes, mountain lions, Columbian mammoths, at least two species of horses, Camelops, deer, and extinct pronghorns (Mawby 1967). Mammoths and camels are most common (Springer et al. 2010). Many other forms are known from the Tule Springs beds, but are not assigned to one of the stratigraphic units. They include several species of toads and frogs, a tortoise, three species of lizards, two snake species, several species of rodents, badgers, and a large bovid (Austin et al. 2005). The saber-toothed cat Smilodon has recently been reported (BLM 2012).

References

Austin, C., K. Springer, E. Scott, C. Manker, and C. Sagebiel. 2005. Additions to the late Pleistocene vertebrate paleontology of the Las Vegas Formation, Clark County, Nevada. Journal of Vertebrate Paleontology 25(supplement to 3):33A.

Bell, J. W., A. R. Ramelli, and S. J. Caskey. 1998. Geologic map of the Tule Springs Park Quadrangle, Nevada. Nevada Bureau of Mines and Geology, Reno, Nevada. Map 113. Scale 1:24,000.

Bureau of Land Management. 2012. Sabre-toothed cat fossils discovered in Las Vegas.

Harrington, M.R. 1934. A camel-hunter’s camp in Nevada. The Masterkey 8(1): 22–24.

Haynes, C. V. 1967. Quaternary geology of the Tule Springs Area, Clark County, Nevada. Pages 15–104 in H. M. Wormington and D. Ellis, editors. Pleistocene studies in southern Nevada. Nevada State Museum, Carson City, Nevada. Anthropological Papers 13.

Longwell, C. R., E. H. Pampeyan, B. Bowyer, and R. J. Roberts. 1965. Geology and mineral deposits of Clark County, Nevada. Nevada Bureau of Mines, Reno, Nevada. Bulletin 62.

Mawby, J. E. 1967. Fossil vertebrates of the Tule Springs site, Nevada. Pages 105–128 in H. M. Wormington and D. Ellis, editors. Pleistocene studies in southern Nevada. Nevada State Museum, Carson City, Nevada. Anthropological Papers 13.

Mehringer, P. J., Jr. 1967. Pollen analysis of the Tule Springs Site area, Nevada. Pages 129–200 in H. M. Wormington and D. Ellis, editors. Pleistocene studies in southern Nevada. Nevada State Museum, Carson City, Nevada. Anthropological Papers 13.

Quade, J. 1986. Late Quaternary environmental changes in the upper Las Vegas Valley, Nevada. Quaternary Research 26(3):340–357.

Ramelli, A. R., W. R. Page, C. R. Manker, and K. B. Springer. 2011. Geologic map of the Gass Peak SW Quadrangle, Clark County, Nevada. Nevada Bureau of Mines and Geology, Reno, Nevada. Map 175. Scale 1:24,000.

Simpson, G.G. 1933. A Nevada fauna of Pleistocene type and its probable association with man. American Museum Novitates 667.

Springer, K., E. Scott, J. C. Sagebiel, and C. R. Manker. 2010. The Tule Springs local fauna: late Pleistocene vertebrates from the upper Las Vegas Wash, Clark County, Nevada. Abstracts with Programs - Geological Society of America 42(5):250.

Springer, K., E. Scott, C. R. Manker, and S. M. Rowland. 2011. Vertebrate paleontology of Pleistocene lakes and groundwater discharge deposits of the Mojave Desert and southern Great Basin. Pages 156–230 in J. W. Bonde and A. R. C. Milner, editors. Field trip guide book, 71st annual meeting of the Society of Vertebrate Paleontology Las Vegas, Nevada November 2-5, 2011. Nevada State Museum, Carson City, Nevada. Paleontological Papers 1.

Spurr, J.E. 1903 Descriptive geology of Nevada south of the fortieth parallel and adjacent portions of California. U.S. Geological Survey, Washington, D.C. Bulletin 208.

Taylor, D. W. 1967. Late Pleistocene molluscan shells from the Tule Springs area. Pages 397–399 in H. M. Wormington and D. Ellis, editors. Pleistocene studies in southern Nevada. Nevada State Museum, Carson City, Nevada. Anthropological Papers 13.

Wormington, H. M., and D. Ellis, editors. Pleistocene studies in southern Nevada. Nevada State Museum, Carson City, Nevada. Anthropological Papers 13.

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