Most people are unaware that California was once populated by tortoises as large as those found on the Galapagos Islands of today, large enough that a person could have literally taken a ride on its back. The remains were found in the Tehama Formation that was deposited in the area when the coast range was beginning an active uplift and debris washed down creeks and rivers to be deposited in the north valley as mud, sand and gravel. These sediments entrapped the bones of numerous animals that were then preserved as fossils. Because the Tehama formation lies above a dated volcanic ash that covered much of the north state about 3.3 million years ago it is assumed that the fossils are about 3 million years old. Only in recent time have these sedimentary rocks been uplifted and now eroded to expose these ancient remains.
The site was once a water hole. The base of the fossil layer has dried up algae. The date of this deposit is shortly after the explosion of the Tuscan Buttes volcano southeast of Red Bluff. 3.2 million years ago it liberated so much volcanic ash that it can be found as far away as New Mexico. It is known as the Nomlaki Tuff, for the area around the home of the Nomlaki Indians where the tuff was found and named. The tuff layer made it difficult for the wildlife to find food and water and probably contributed to the concentration of dead animals at this location.
These remains were discovered by local hunters Mike Higley (on the right in the photo) and John Rhea Jr. (on the left in the photo). The excavation team members were Richard Hilton, Charles Dailey, and museum technician George Bromm. Volunteers at the site included John Rhea Jr., Mike Higley, Patrick Antuzzi and James Readle.
Found in the vicinity of the tortoise were the partial remains of a large extinct cat that was bigger than a bobcat but smaller than a mountain lion. Other fossils included those of horse, deer, camel, bear and even a pond turtle. In other areas the Tehama Formation has yielded additional animal remains, giving us a clearer picture of the 3 million-year-old ecology. These include mastodons (extinct relatives of elephants), hyena-like dogs, giant ground sloths (who originally made their way here from South America) and various species of rodents and birds.
These tortoise remains may be the most complete of any of the giant tortoises found in California and according to fossil turtle and tortoise specialist, Dr. James Parham, they may be of an as yet undescribed species.
Giant tortoise had a wide distribution around the world, including many isolated island groups. Their distribution is best understood in the context of continental drift after fragmentation of the early Mesozoic supercontinent Gondwanaland.
An additional giant tortoise was found in southeast Oregon and one more in Anza-Borrego State Park. This may be an undescribed species. Ours has a flat lower plate (plastron). Males typically have a concave plastron that allows them to get closer to the females for mating, so ours is probably a female. However it is as large as many of the males from the Galapagos Islands east of Ecuador. A few of the bony plates of the dorsal shell (carapace) are clay replicas of the mirror image real plates from the other side.
Under the giant tortoise in the east foyer display case are numerous other turtles and tortoises found on other Summer field class fossil collecting trips.
Find out more about turtles and tortoises through the California Turtle and Tortoise Club.
Our first excavation expedition was shortly after the 9-11 attack on the United States, and one of the train engineers was nervous about people with picks and shovels near the train tracks. He called railroad security and despite our permission to be there he had us excluded from the site. 15 years later we got to return and the jaw of an extinct Spectacled bear was found.