Local history books tell about the early settlers in the San Ramon Valley and, before that, the Native Americans living along the creeks. But go back another 10 million years – to prehistory. At the time, long-necked camels, rhinos, wild horses, saber-toothed cats and mastodons existed in an ecosystem that more closely resembled the Africa savanna than our wooded suburbs would suggest.
The remains of these creatures, discovered in Danville, are now part of the latest exhibit at the Museum of the San Ramon Valley, “Beasts in Your Back Yard.” The centerpiece of the exhibit is a full-scale replica of an ancestral mastodon “Gomphotherium simpsoni” skeleton. The exhibit also includes the skull of a saber-toothed cat and other bones and fossils found in the Blackhawk Ranch quarry, which has a reputation as the richest archeological site of vertebrate fossils in the San Francisco Bay Area.
The Blackhawk Ranch treasury of fossils was discovered in 1926 by Bruce Clark, a geologist for the University of California, while he was creating a soil map of the Mount Diablo region. While Clark was in the area, ranch hands told him there were “dinosaur bones” in the area. Clark investigated, realized that the soil samples were 10 million years old, and determined it was a fossil locale.
An extensive dig led by UC paleontologist K.A. Richey was done of the site in the 1930s, as a part of the Public Works Administration program. Richey and his team discovered fossils dating back to the Miocene period, 5.3 million to 23.8 million years ago. Those fossils are now located at the UC Museum of Paleontology (UCMP) in Berkeley, which houses the largest collection of fossils of any teaching university in the world, including microfossils, fossil plants, vertebrates and invertebrates.
The story the fossils tell is a fascinating peek into our prehistoric past. In the Miocene period, Danville and surrounding areas could have been mistaken for Africa, in regards to both the animals that lived here and the environment. The climate was mild, without seasons, and the terrain was grassy plains. However, many of the trees were similar to those that grow here now – elms, poplars, oaks and sycamores.
Twelve-foot-tall camels, with necks like giraffes, and three-toed horses fed on the grasses and abundant foliage. Other, more familiar animals also existed, including rabbits, beavers, squirrels, foxes and relatives of modern-day raccoons and turtles. The most prevalent predator was a hyena-like dog (Borophagus) with sharp, powerful teeth and a jaw like a coyote.
The largest of the fossils was the Gomphotherium, or mastodon, which is related to mammoths and modern elephants. Unlike the mammoths, the mastodons were not covered with long hair, but with short fur. Mastodons were about 10 feet tall and ate plants. They had two sets of tusks, and used their smaller, lower tusks like a shovel to scoop up plants from streambeds where they fed. Mastodon trunks were not as long as those of mammoths or elephants but muscular and flexible, which they used as we use arms and fingers.
After Richey’s team finished its dig in the 1930s, UC undergraduates, paleontology graduate students and museum staff continued to make fairly regular trips to the quarry, although it was no longer an active excavation site. In 1987, Ken Behring, the developer of Blackhawk, officially donated the quarry to UCMP.
In 1991 the Blackhawk Museum, in conjunction with UCMP, decided to revisit the quarry. Dan Dunn, director of the Blackhawk Museum, had had archeology training in college and knew how to run a dig site. He launched a community dig supervised by the UCMP, with support from UC Berkeley students and small groups of museum members.
“We had an interest in going back through Richey’s work and trying to identify some of the smaller animals,” said Dunn. “We knew we had an entire ecosystem there. The public was interested in finding mastodons, but we were interested in finding aquatic turtles, fish and small mammals.”
Mark Goodwin, assistant director for Research and Collections at UCMP, explained why the Blackhawk quarry is so rich in fossils.
“The rocks at the quarry represent an ancient stream system that flowed across a broad alluvial plain toward the ancestral bay,” he said. “Ten million years ago, this ancient streambed was near sea level. Natural sorting occurs as the rivers and streams deposit the sediment and the bones they carry along the stream banks during flooding, and in the streambed as the bones settle out.”
“One of the interesting things about the quarry is that you end up with stuff just piled on top of one another,” Dunn added. “Animals that wouldn’t be anywhere near one another are found within inches of each other there.”
Because of the nature of the site, the fossils that were used to create the ancestral mastodon replica that is currently on exhibit at the Museum of the San Ramon Valley came from several different animals found at the site and collected in the 1930s.
“We didn’t find the whole fossil on the hill like you see in the National Geographic,” said Dunn.
The latest dig succeeded in finding many smaller fossils in addition to adding to the mastodon fossils that Richey’s team and other UC Berkeley paleontologists had uncovered. Goodwin supervised the construction of the composite mastodon model by making molds from the original fossils found at the quarry, then casting them in a durable plastic resin. The mastodon was on display for several years at the Blackhawk Museum.
Mastodons became extinct about 11,000 years ago, although they vanished from our local area millions of years before, most likely due to extreme climate change. Nobody knows exactly why mastodons died out, but educated guesses include over-hunting by humans, environmental causes related to climate change, and highly infectious diseases.
What we do know is that the story told by the fossils found in the quarry gives us a glimpse into what it was like in our own back yard millions of years ago.
“One of the great functions of the quarry,” said Dunn, “is that it helps explain to people what they are finding when they’re digging in their flower beds. When they find sand dollar imprints, they’ll understand why.”
Fun fossil facts
* Mastodons and the other fossils found locally are prehistoric animals, not dinosaurs. Dinosaurs became extinct at the end of the Cretaceous period, about 65 million years ago. The Mount Diablo region was never home to dinosaurs because it was under water during the Jurassic and Cretaceous periods. The closest dinosaur bones were found near Pacheco Pass in central California.
* Since Miocene times, there have been approximately 22 different types of elephants. Only two types – the Indian and African elephants – are living today.
* The official state fossil of California is the Saber Tooth cat, or Smilodon. Although there is no evidence that the Smilodon lived in this area, other smaller, saber-toothed cats did.
* Many people mistakenly think that Mount Diablo was once a volcano, because lava rock can be found on the mountain. However, the lava came from the sea, upwelling from deep in the earth through fissures in the ocean crust, and from neighboring volcanoes in the Berkeley Hills. Mount Diablo, at 3,849 feet, is relatively young, having risen as the result of seismic activity over the past 2 million years.
* In California, any fossils found on private land belong to the property owners, so remember to ask permission before you start looking. Fossils on government land, state and national parks, are protected by a variety of laws and a scientific permit is required. The fossils must be deposited in a proper scientific repository or museum, such as the UC Museum of Paleontology.
* The UCMP is not open to the public, but special tours for schools and youth groups can be arranged. Each April on Cal Day, the UC Berkeley campus opens its doors to visitors who enjoy hands-on activities, lectures and more. UCMP participates by offering a variety of activities for paleontology buffs of all ages. This year Cal Day is April 22. For more information, visit http://www.berkeley.edu/calday/ or call (510) 642-5215.@12sub:Local fossils and more
What: “Beasts in Your Back Yard”
When: Now through April 22
Where: Museum of the San Ramon Valley, corner of Railroad and Prospect avenues in Danville
Telephone: 837-3750
Admission: Free, but donations are appreciated
Museum hours: 1-4 p.m., Tuesday-Friday
10 a.m.-1 p.m. Saturday
1-4 p.m. Sunday, March 16-April 22
