Travel through time to a paleo-botanical discovery in Sugarloaf’s Sonoma Creek

In his 40 years as senior state archaeologist at California State Parks, Breck Parkman has conducted hundreds of digs in 90 Northern California parks that have fascinated the public. He’s unearthed remarkable cultural and natural artifacts, from as recently as the 1960s hippie era to as far back as thousands of years ago, when our landscape looked perhaps much different than it does today. At Fort Ross in the late 1990s, he led a UNESCO-sponsored project that brought together American and Russian school children to study the fort’s archaeology. He’s explored “rubbing rocks” along Sonoma County’s coast he believes mammoths used to groom themselves. And over the last 15 years, he’s been digging beneath the surface at Sugarloaf Ridge State Park.

Parkman talked recently with writer Kathleen Scavone about what he’s discovered at the popular park and what it tells us about our landscape thousands of years ago.

This interview was edited for brevity.

Q. When did you begin exploring in Sugarloaf?

Following the New Year’s Eve Storm of 2005-2006, I spent weeks surveying the local parklands, walking the recently swollen creeks and riverbanks. Flooded waterways are destructive. They can cause substantial erosion and property loss. The New Year’s Eve Storm was no exception. Flood events like this are also revealing. I wanted to see if previously unknown archaeological sites had been revealed by the floodwaters. As I surveyed the ravaged creeks and waterways, I found bits and pieces of the area’s archaeological record. ... I got my feet wet, but it was worth it.

Perhaps the most unique discovery I made was the paleo-floral deposit I discovered on Sonoma Creek, within Sugarloaf Ridge State Park. At one location, I found numerous specimens of partially carbonized wood eroding from a deeply buried deposit. This paleo-floral deposit was at least 90 centimeters thick and consisted of a blue clay stratum about 6 meters below the top of the bank on the right side of the creek. It’s likely that the deposit of blue clay extends below the current base of the creekbed.

The deposit appears to be associated with an area of land subsidence on the slope immediately above the creek. The scar of the slide can be seen extending quite visibly about 100 meters up the hillside. It’s apparent that this is not a recent slide. I suspect it dates to more ancient times. In fact, I believe that it’s likely that the slide created the paleo-floral deposit at the edge of the creek.

Upon discovering the site, I spent the next day or two working on its documentation and collecting a small handful of samples of the paleo-floral specimens I could see eroding from the blue clay stratum. I suspected that the blue clay was associated with the ice age, but I couldn’t confirm it at the time.

While most of the paleo-floral specimens I recovered consisted of sections of limbs and twigs and large pieces of tree bark, over 100 small redwood and Douglas fir cones were recovered from the blue clay as well. All the specimens are partially carbonized. A single cone of what appears to be California juniper was also found in the deposit. But what really excited me was the discovery of six pine cones, most which appear to be Monterey pine.

Q. Why was that discovery significant?

I obtained two radiocarbon dates from fossil wood samples derived from the deposit. The samples were dated by Beta Analytic Testing Laboratory, a radiocarbon dating lab in Miami. One date came from near the top of the fossil deposit. The other came from near the base. Both of my dating specimens were parts of twigs. The upper date came back as being about 18,000 BP (before the present). The lower date was about 27,000 BP.

Those dates excite me because they overlap what scientists call the last Glacial Maximum. The Last Glacial Maximum marks the final cold spell of the last ice age, at which time the polar ice caps and glaciers had advanced as far as they would go. Following the Last Glacial Maximum, the world began to warm, and the ice began to melt and withdraw.

Q. You said you consulted with a variety of experts about your findings. How does your discovery at Sugarloaf relate to your other work, especially along the Sonoma Coast?

When the last ice age occurred, we need to picture the land as it teemed with mammoth, mastodon, camel, horse and more. ... The pine cones help fill in a part of the puzzle regarding what our area looked like near the end of the last ice age.

The Monterey pine grew on our local Sonoma Coast and were present in the Mayacamas Mountains, which were then over 60 miles inland as well. Following the end of the ice age, the territory of Monterey pine shrank toward the south, to its present-day range around Monterey and Ano Nuevo. At the same time, the Sitka spruce that occurred on our coast withdrew northward to the Northwest Coast.

This was when the mammoth and other Rancholabrean megafauna were going extinct. Broad global changes in weather have serious consequences, as we are beginning to see today. In understanding the “California Serengeti,” it’s necessary to picture the landscape. Where were the forests and what were they composed of? And were the interior valleys and coastal plains grassy pastures?

The Rancholabrean megafauna consisted largely of grazers (for example, mammoth and bison) and browsers (for example, mastodon and giant ground sloth). To some extent, I’ve tried to correlate known fossil discoveries with what we know about our local Pleistocene landscape. For example, I would expect to find mammoth fossils in the valleys and on the plains, not up in the hills, and that’s exactly what the data suggests. The mammoth was a grazer and spent its time in the lush pastures that were our local valleys and plains. The mastodon was a browser and the discovery of its fossils in areas assumed to have been woodlands makes sense to me.

The ancient pine cones from Sugarloaf help me picture the Late Pleistocene landscape that was found in the interior. And that helps me predict where certain kinds of fossils might be found and how the megafauna might have moved seasonally. It also helps flesh out my storytelling! And I love to tell stories about the ice age!

Q. What does this tell us about climate change now?

The discovery provides an important perspective on the forests of the Mayacamas Mountains during the Late Pleistocene. It also has the potential to help inform our knowledge of the challenges that face us in these times of global climate change.

The riparian zone found along the upper Sonoma Creek watershed is today home to stands of coast redwood and Douglas fir. The discovery of fossil plant remains from these two species is not unusual. However, the discovery of the pine cones does appear to be significant. The only native pine found on upper Sonoma Creek today is the gray pine. The ancient cones I found in the blue clay deposit are from a different species.

I believe the six pine cones I found on Sonoma Creek might have significance in a world that is now struggling with a changing climate. Future efforts to better date the six cones and to establish their genetic history are called for. Given that at least one of the cones shows clear evidence of ancient bark-boring beetle activity, that might prove another area for future study.

The ancestral Monterey pines of Sonoma Creek were forced to migrate to survive. The Columbian mammoth and many other species of Rancholabrean megafauna were unable to find a suitable refuge and, as a result, went extinct. Today, various plant and animal species are facing a similar decision. Migrate or perish. In certain parts of the world, human communities are being forced to take flight as well.

Parkman worked with Doshia Dodd of Sonoma State University, who joined him in studying Sugarloaf’s ancient pine cones. They endeavored to identify all six of the cones and visited the California Academy of Sciences in San Francisco to use their botanical collection for comparisons. They reconfirmed that the cones they felt to be Monterey pine were indeed just that, since, as Parkman said, “The cones of this species are distinctive and one of the easiest to recognize. They are asymmetrical with large, smooth, knoblike protuberances on the scales. The scales do not have sharp prickles like some pine species.”

Not every pine cone found on Sonoma Creek was easy to identify, however. Parkman noted that some look to be possible hybrids, and may have been derived from a cross between Monterey pine and some other species, such as bishop pine or knobcone pine. He is looking forward to future efforts to better identify the hybrid pine cones found.