The Frenchman Hills – Tonnemaker Mammoth Site is owned and operated by Tonnemaker Hill Farm of Royal City, Washington.

The MCBONES Research Center Foundation oversees research and education at the site.


In March 2015, Luke Tonnemaker unearthed some large bone fragments while moldboard plowing up an alfalfa field (to prepare it for replanting) on the north side of Frenchman Hills in Grant County, Washington.

Mammoth Bone Discovery


Exploratory excavation recovered a number of bone fragments in the top 75 cm (2.5 ft) of the soil profile.

Exploratory Excavation of Bone Fragments

The largest bone fragment was tentatively identified as a mammoth tibia.

Excavated Bone Fragments


Additional bones were found about 12 m (40 ft) away. Excavations were expanded on March 28, 2015 to include the new findings. Note the location of the mammoth’s skull in the lower left corner of photo below.

Expanded Excavations and Mammoth Skull

Formal excavations were concluded on April 19, 2015 with extraction of the skull (below). The top part of the mammoth skull was recovered. Although it was missing the tusks, it was obvious where they should have been (bottom of photo).

Recovery of Mammoth Skull

Kole and Luke Tonnemaker continued to excavate the site and recover additional bones every opportunity they had as long as it did not interfere with their primary farming operation. Over 150 field specimens have been collected.


Work continues to clean, preserve, reassemble, document, and interpret the many recovered mammoth bones. Note the fibula on the right. Radiocarbon dating of samples from the tibia were unsuccessful due to the presence of modern alfalfa roots that had penetrated into the specimens.

Laboratory Studies and Identification of Mammoth Bone Fragments
tonnemaker_cleaning tonnemaker_fibula


Geologic research has included trench logging, borehole sampling, tephra (volcanic ash) analysis, X-ray fluorescence analyses, and optically stimulated luminescence (OSL) analyses.

Geologic Research of Material Around Mammoth Bones

Preliminary analysis of samples from three tephra (volcanic ash) layers (XU2-23 through -25) suggested that the lower most samples were likely to be of Mount St. Helens set “S” ash dated at ~13,600 to 12,500 C14 yrs BP) and that the mammoth bones could be as young as 10,740 C14 years BP (Amara 2016, Dodd et al. 2016).

Soil Column of Area Around Mammoth Bones

Frenchman Hills – Tonnemaker Mammoth Site Research Bibliography


Last, G. V., K. Newhall-Perry, R. Faubion, N. L. Mara, and B. R. Barton. 2020. Case Report of an Abnormal Mammoth Rib from the Frenchman Hill – Tonnemaker Mammoth Site, Grant County, Washington. Northwest Scientific Association Program and Abstracts, March 2020, Eugene, OR., p. 44.


Amara, M. S., G. V. Last, L. Tonnemaker, K. Tonnemaker, and B. R. Barton. 2019. Late Pleistocene Mammoth Remains and Their Geologic Context in the Frenchman Hills, Grant County, Washington. Northwest Scientific Association Program and Abstracts, March 26-29, Lewiston, ID., p. 24.


Amara, M. February 2018. “Age Analyses and Theories of Locally Discovered Mammoth.” In Coulee Corridor Byway Beat. Volume 6, Issue 1. Coulee Corridor Consortium.


Last, G. V., M. S. Amara, F. F. Foit, Jr., O. K. Neill, T. Rittenour, J. L. Dodd, K. Tonnemaker, and L. Tonnemaker. 2017. Tephra and OSL Results from the Frenchman Hills – Tonnemaker Mammoth Site, Royal City, Grant County, Washington. Geological Society of America Abstracts with Programs. Vol. 49, No. 6. doi: 10.1130/abs/2017AM-304854


Amara, M. 2016. “Ancient Mammoth Unearthed” in Coulee Corridor Byway Beat. Volume 5, Issue 1, March 2016, p. 3-4.

Dodd, Jessica L., George V. Last, Mark Amara, Kole Tonnemaker and Luke Tonnemaker. 2016. “Tephra Chronology of the Frenchman Hills - Tonnemaker Mammoth Site: Shedding light on its Geologic History.” Northwest Scientific Association Program and Abstracts, March 23-26, Bend, OR, p. 51.