Osborn Preserve

Student studying near creek

Size & Location 450-acres, Penngrove, Sonoma County
Directions & Parking PDF icon Written Directions to Osborn & Parking Information / Google Maps to Osborn (Reservation Required)
Data & Images Data
Interactive Map Osborn Arc GIS
Current Weather National Weather Service - Osborn Preserve


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The 450-acre Fairfield Osborn Preserve lies on the northwest flank of Sonoma Mountain in Sonoma County, California. The preserve ranges in elevation from 1350 to 2300 ft and is characterized by active slumps and landslides and basalt exposures. Copeland Creek, a perennial drainage at upper elevations, drains into the Laguna de Santa Rosa in the Russian River watershed. Eight plant communities include upland, riparian and freshwater marsh habitats. The preserve is located in Penngrove and is a 15-minute drive from the SSU campus.


Preserve climate is typical of Mediterranean regions, with cool wet winters and hot dry summers. The majority of rainfall comes from atmospheric rivers that transport moist air to the Sonoma Coast from the tropics. Proximity to the Pacific Ocean moderates seasonal extremes: snow is rare and summer temperatures rarely exceed 100 F. In the summer, fog frequently moves inland along valley bottoms, leaving the upper slopes of the mountain exposed.

Geology & Soils

Preserve soils are predominantly Goulding clay loam with extensive areas of basalt exposures. Typical soil depths are 16 to 20 inches and often occur on slopes of 15 to 45 percent. Widespread rhyolite creates highly erosive geology that occurs as slumps and landslides throughout the preserve. On the higher drier slopes, terraces of Raynor clay are associated with seeps and higher moisture retention at Turtle Pond and Cattail Marsh. The Rodgers Creek fault is about 2 miles west of the preserve and numerous side branches intercept the preserve.


Preserve lands span the Copeland Creek, Mark West and Petaluma watersheds. Both Copeland and Mark West drainages discharge into the Laguna de Santa Rosa, a 14-mile long wetland complex listed as a wetland of international importance by the Ramsar convention. The Preserve protects roughly one mile of a perennial section of upper Copeland Creek and seasonal drainages. Seasonal and perennial ponds and marshes are created by clay soils and springs. The freshwater marsh may have been formed by massive land movement along the Rodgers Creek Fault. Two perennial ponds on the property are manmade.


Principal plant communities within the Preserve are the oak woodland, chaparral, freshwater marsh, native and non-native grasslands, douglas-fir woodland, and riparian woodland.

Oak woodlands are dominated by coast live oak (Quercus agrifolia), California black oak (Quercus kellogii), and California bay laurel (Umbellularia californica) and the understory includes toyon (Heteromeles arbutifolia), coffeeberry (Frangula californica) and poison oak (Toxicodendron diversilobum). Grasslands in some areas still contain a rich array of native grasses and forbs. Perennial riparian zones of Copeland Creek have a high percentage of California bay laurel and also include big leaf maple (Acer macrophyllum), hazelnut (Corylus cornuta), and alder (Alnus rhombifolia).  The deeply shaded understory contains snowberry (Symphoricarpos spp.) and the uncommon California ginseng (Aralia californica).


Animal diversity on the preserve is high due to the availability of year-round water. Perennial sections of Copeland Creek support yellow-legged frog (Rana boylii) rough-skinned newt (Taricha granulosa) and California giant salamander (Dicamptodon ensatus). Natural and man-made ponds are critical habitat for the federally-listed red-legged frog (Rana draytoni), and additionally support California newt (Taricha torosa), western pond turtle (Emys marmorata), and -- on occasion -- river otter. Non-native bullfrogs (Rana catesbeiana) occur in some ponds and are a threat to native species. The freshwater marsh is important habitat for sora and Virginia rails and other birds.

Top predators are still present and include mountain lion (Puma concolor), golden eagle (Aquila chrysaetos), coyote (Canis latrans), bobcat (Lynx rufus) and gray fox (Urocyon cinereoargenteus).


For thousands of years, Sonoma Mountain has been a place of meaning, knowledge, and connection for Coast Miwok & Southern Pomo people—the descendants of whom today are enrolled citizens of the FederatedIndians of Graton Rancheria (FIGR, Tribe). As the original inhabitants and stewards of the landscape, FIGR maintains an interest in sustaining the cultural landscape and continuing an enduring relationship with the land.

When the Homestead Act passed in 1862, settlers claimed the lands and eventually sold it to families harvesting firewood or grazing cattle and sheep. In the 1950s, Joan and William Roth purchased the property as a summer vacation home and weekend retreat. In 1972, they donated the southern 200 acres of the property to The Nature Conservancy (TNC), naming the property after Joan’s father, Fairfield Osborn Jr., a pioneer in environmental conservation. TNC ran outdoor education and docent training programs for 25 years. In 1997, TNC donated the property to SSU under a conservation easement. An additional 210-acre donation from the Roth family nearly doubled the Preserve’s size in 2004 and a final donation of 40 acres was made in 2013.

Since 1997, Preserve lands have been managed by SSU’sCenter for Environmental Inquiry (CEI, previously known as SSU Preserves). These lands serve as training sites to reconnect people of all backgrounds with the ecosystems that support them and as sites for hands-on training. They are open to anyone engaging in research and education activity. Recreational activity is not allowed as a condition of the land donation agreement.


The Marjorie Osborn Education & Research Center (2,100 sq ft) has two meeting rooms for educational and research use, conferences and meetings. The larger room seats up to 24 people and includes a high-definition screen. The smaller room seats up to 15 people and has a small kitchenette that includes a small refrigerator and sink.

Substantial renovations to the facilities were made possible in 2023 by a generous donation from the Federated Indians of Graton Rancheria. The renovation includes development of outdoor seating areas, and upgrades to parking, signage, safety and accessiblity.

A wireless sensor network broadcasts data from weather stations and cameras to the internet and allows for virtual visits by classes and researchers. The trail system provides good, though sometimes rugged, access to most areas of the Preserve.


Research at the Osborn Preserve includes independent studies conducted by researchers and Preserve-coordinated efforts that target management needs. These studies have investigated diversity of phenomena including disease, invasive species, cultural surveys, and plant physiology. A detailed study of aquatic insects by Larry Serpa during the 1970s is a significant resource for researchers studying riparian communities. The Preserve may be best known for the intensive work on Sudden Oak Death conducted since the disease was first found in California in 1995.


The Preserve is open for research and educational programs, and public visitation is permitted by guided tour only. Management issues, such as invasive species control, erosion and sudden oak death, are representative of regional land management issues and create opportunities for collaborative efforts with researchers, students, agencies and organizations. As much as possible, management results are shared with students, landowners, managers, and policymakers to highlight successful techniques that conserve natural processes.