What’s down deep
A convergence of plates
Beneath the oak woodlands, expanses of wildflowers, and trickling seeps that make Patwino Worrtla Kodoi Dihi Open Space Park lie volcanic rocks formed 3 to 5 million years ago when the crux between three different tectonic plates crushed its way through what is now Solano County. Known as the Mendocino Triple Junction, this geological friction point is where the Pacific plate, North American plate, and Gorda plate converge. As it rumbled beneath thin points in the Earth’s crust in the area, the junction’s passage unleashed a complex series of lava flows known as the Sonoma Volcanics.
The Sonoma Volcanics spewed multiple times over an area encompassing more than 350 square miles, from what is now Interstate 80 to Mount Saint Helena and west toward Petaluma. Most of the rocks found in Patwino Worrtla Kodoi Dihi are Sonoma Volcanics deposits, including minerals such as rhyolite, andesite, basalt, and deposits of volcanic ash called tuff.
“At one point, the Earth was alive with the movement of the Mendocino Triple Junction going right through that area,” says Mike Wray, geologist and neighbor of the open space.
Over the last 25 million years, the Mendocino Triple Junction has moved north, from its origin north of Los Angeles to its current location beneath Mendocino County, lengthening the famous San Andreas Fault in its wake. The Cordelia Fault, an eastern offshoot of the San Andreas fault zone, passes through the open space. A roadcut right of the park entrance reveals a cross section of the fault, with exposed layers of pumice and other volcanic materials.
“It’s the most visible, most striking fault exposure in the Bay Area,” says Wray.
Meanwhile, the valleys below the rolling hills of Patwino Worrtla Kodoi Dihi Open Space Park contain alluvial deposits: clay, gravel, and silt left behind by centuries of erosion.
“We’ve got volcanics. We’ve got fault lines. We’ve got metamorphics,” says Jasmine Westbrook Barsukov, stewardship manager for Solano Land Trust. “It’s all sorts of fun out there.”
A Walk in the Park with the Patwin People
The Yocha Dehe Wintun Nation’s tribal chairman welcomes the public to 1,500 acres of oak woodlands in Solano County.
If you go
Patwino Worrtla Kodoi Dihi Open Space Park
Trails: Fourteen miles of trails are available to hikers, mountain bikers, and equestrians.
Hours and entrance: 9 a.m. to 5 p.m., Friday through Monday. Parking is $5 per vehicle and $10 per horse trailer. Solano County Parks offers an annual pass and honors the State of California Golden Bear Pass, which provides access to parks across California.
Address: 2061 Rockville Road, Fairfield 94534
Facilities: The quarter-acre Welcome Plaza by the parking lot has pit toilets, potable water, wheelchair-accessible picnic tables, a native plant garden, and shade. Both the Welcome Plaza and the 0.6-mile All People’s Trail loop are equipped with ADA-accessible park tread. Dogs are not allowed on the property.
What grows above
Wildflowers galore, and more
Minimal soil and the area’s extensive layers of bedrock make great habitat for endemic specialists while being inhospitable for many invasive species. One of the healthiest blue oak woodlands remaining in the region grows here, according to Barsukov. The oaks have adapted to thin soil by growing shallow, spread-out root systems, although they are vulnerable to trampling and erosion. Solano Land Trust volunteers and staff have planted blue oaks to restore more of the woodland, using enclosures to protect acorns and seedlings from hungry feral pigs.
Besides oak woodlands, the open space is home to pockets of chaparral along ridges and small seasonal wetlands known as seeps. During the rainy season, water flows over the bedrock, trickling along to form shallow, temporary wetlands. Seeps share some species in common with vernal pools, such as moss pygmy weed (Crassula connata), a nubby succulent, and bright yellow, red-freckled seep monkeyflower (Erythranthe guttata). Common meadowfoam (Limnanthes douglasii), a wildflower that flourishes in seeps, produces a buoyant fatty acid similar to whale oil to spread its floating seeds.
“We have so many seeps,” says Barsukov.
Left: Moss pygmyweed (Valentino Traversa, CC BY-NC via iNaturalist); right, seep monkeyflower (Alex Abair, CC BY-NC via iNaturalist)
As winter gives way to spring, March is the peak season for wildflowers that paint the hillsides and thrive in the seeps. Seep monkeyflower, goldfields, sky valley lupine, and popcorn flower adorn the hills in pops of orange, yellow, white, and blue. From the All People’s Trail, native larkspur, lewisia, and clarkia flowers add touches of purple and pink.
The open space is also home to the rare nodding harmonia (Harmonia nutans). Each spring, a group of Solano Land Trust volunteers get on their hands and knees to tally up the number of the six inch tall flowers growing within the park. Counting them is tricky—goldfields, a much more common wildflower, are close lookalikes. But goldfields have round petals, while the nodding harmonia petals have three small lobes on the ends.
“Only four counties have it at all, and it’s only in two places in our county,” says Barsukov. “Despite that, it still doesn’t have any state or federal protections.” The land trust monitors the nodding harmonia population in the open space to help inform how well they are supporting the species, and to provide data should the species ever be considered for protection.
In late spring, the wetter parts of the park teem with baby amphibians. Ponds on the property are breeding habitats for California toads and newts. On a hike in May, Barsukov witnessed a parade of quarter-sized California toads (Anaxyrus boreas halophilus) with white stripes on their backs hopping across the trail.
Left: California toad (Anaxyrus boreas halophilus) (Marc L., CC BY-NC via iNaturalist); right, Dutchman’s pipe (Kathy, CC by-NC 2.0 via Flickr)
On the Overlook Trail, visitors might glimpse Dutchman’s pipe tangling and trailing along the ground. Dutchman’s pipe comes from a family of carnivorous pitcher plants, but the soil here is nutritious enough that this species no longer devours insects. Instead, it has formed a symbiotic relationship with the caterpillars of California pipevine swallowtail butterflies.
These caterpillars exclusively eat the leaves of Dutchman’s pipe, which makes them toxic to predators. Dark orange when young and then studded with striking orange-tipped black spikes, these caterpillars aren’t shy about announcing their venomous nature as they munch their way through the underbrush. The caterpillars metamorphose into iridescent black and blue butterflies adorned with little orange spots. While California pipevine swallowtails are abundant at Patwino Worrtla Kodoi Dihi, they are not found outside the state.
“It’s endemic to California, it can only live here,” says Barsukov. “That species and its host are underappreciated little treasures of our region.”
A park that’s a community project
Solano is the only county in the Bay Area without a parks district. To make parks in Solano County more inclusive and welcoming to different communities, the Solano Land Trust formed partnerships with various community organizations to develop and design the open space. The Trust collaborated with the Yocha Dehe Wintun Nation to name the open space and its trails in the Patwin language. A community input project gathered feedback from Solano County senior centers, educators, and disability advocacy organizations in an effort to design park infrastructure where visitors feel safe, independent, and welcome.
“The community does have a sense of partnership, not just with us, but with the park,” says Nicole Braddock, executive director of the Solano Land Trust. “So much of it is bringing people together, and the land is a great way to do that … Land connects us all.”
