THE CACTUS SPRINGS MAMMOTH TUSK AND MOLAR SITE, CLARK COUNTY, NEVADA

A segment of mammoth tusk, along with a complete molar, was discovered in the spring of 2015 within a Nevada Department of Transportation (NDOT) right-of-way, adjacent to U.S. Highway 95, about 60 km northwest of Las Vegas. The site is a few km west of the abandoned hamlet of Cactus Springs. No vertebrate fossils had previously been reported from this area, although the newly created Tule Springs Fossil Beds National Monument is located just a few tens of km away, to the southeast, within the same topographic depression.

We were alerted to the site by an observant passer-by who noticed a few cm of the tusk exposed in the sloping wall of a man-made drainage channel adjacent to the highway. We found the molar three meters from the tusk when we visited the site. Under permit from the Bureau of Land Management and NDOT, we excavated both the tusk and molar in October of 2015. The tusk turned out to be a short segment, about 40 cm long and 8 cm in diameter, including the distal end. The molar is 18.2 cm long and 7.4 cm wide at the widest point, consisting of 12 enamel plates. It is a maxillary molar, and the dimensions and number of plates indicate that it is a small M4. All of the plates were “in wear” when the animal died, which indicates that the animal was about 12 years old. We hypothesize that the tusk and molar came from the same animal; based on the small size of both fossils, it was probably a female. Both the tusk and the molar appear to have been heavily weathered prior to burial. These fossils were probably exposed on the surface for some time, and transported by stream flow to this location. No other vertebrate fossil material was found at the site, with the exception of a piece of mammoth enamel plate several tens of meters away.

The fossil-bearing horizon, which was exposed when the drainage channel was created some years ago, is 2.2 m below the modern desert surface. The matrix consists of light gray, silt-dominated, groundwater discharge deposits similar to those in Tule Springs Fossil Beds National Monument. Tiny planispiral and conispiral freshwater gastropods, together with the tiny freshwater pelecypod Pisidium, occur in the matrix. On-going research will involve an attempt to date the mammoth fossils and paleoecological analysis of the matrix and mollusks. The fossils will be reposited in the Las Vegas Natural History Museum.