Monumental Questions - Can I still get Poison Oak in the Winter?

Kristie Ehrhardt • February 6, 2025



YES!


Leaves of three - let them be. Right but it’s winter and what if there are no leaves? 

 

Poison Oak (Toxicodendron diversilobum), Pacific Poison Oak or Western Poison Oak is a widely distributed woody shrub or vine that belongs to the Sumac (Anacardiaceae) family. The Sumac family is also known as the Cashew family which contains the tree that gives us that delightful buttery nut (it’s actually a seed) as well as the tree that provides mouthwatering mangos and the tree that produces savory pink peppercorns. How can such a delectable family also give us such an annoying plant? 

 

Poison oak (PO) is not even remotely related to oaks but the leaves sort of resemble oak leaves. They are divided into three leaflets that are about one and a half to four inches long. The species name, diversilobum, refers to the diversity of leaf size and shape; the edges can be toothed, scalloped or lobed and vary greatly. PO is deciduous and the new leaves are usually dark golden or bronze when they are just beginning to unfold in early to mid-spring. They turn a bright then darker glossy green and ultimately transitioning a stunning scarlet red then fading to pink in late summer and fall. The small flowers are greenish-white and appear in late spring to mid-summer and if they are fertilized they become small creamy white berries. Growth forms vary depending on where it is occurring, but it thrives in full sun as well as shady environments. In open sunlight it can grow as a tall, dense shrub or tree with a thick trunk, or a woody vine winding around and up into the canopy of tall trees, fences and other vegetation. In shady areas it can occur as a dense thicket, vine or anything in between. It is prolific and spreads by seed dispersal and through underground rhizomes.

 

It is widely distributed in Western North America from British Columbia, Washington, Oregon, California, Nevada and Baja Mexico and occurs extensively throughout the Berryessa Snow Mountain National Monument. It occurs in chaparral and woodland habitats as well as coastal sage scrub, grasslands, oak woodlands and mixed evergreen forests below 5,000 feet. It’s a common understory plant in riparian corridors and grows alongside Giant and Coastal Redwoods. PO is even a constant quagmire in dry-farmed mountain orchards, urban parks and recreation areas. In fact, it’s kind of hard to find a biome in the Central Valley of California that doesn’t support Poison Oak unless you go into the Great Basin or the southwestern edge of the Mojave desert.

 

The genus Toxicodendron contains many plants that cause allergic reactions. The oil of the plants contains a compound called Urushiol that causes the reaction and it is found in all parts of the plant except the pollen (ironic!). Direct contact with the plant or anything that has touched the plant such as clothing, pets, tools or vehicles can result in painful, itchy blisters. Not everyone is allergic to it, however, repeated exposure can lead to heightened sensitivity. If an area dense with PO is burning, inhaling the smoke can cause a severe internal reaction.

 

Which leads me to why you can still have a reaction to PO in the winter after all the leaves have fallen. It’s a lot harder to spot when it’s just a twig, branch or bare vine along the edge of the trail. Twigs and stems still contain the oil that produces reactions and you may not even realize that you’ve brushed up against it until it’s too late. Keep an eye out for exposed, reddish-brown whip-like sticks coming out of the ground, especially if you know you’re in an area where PO is present. Sometimes the berries remain on the plant even though the leaves have fallen off and occasionally the stems show black marks where the sap may have oozed out and dried. If you know you’ve been in contact with PO, washing your exposed skin with dish soap is a great way to remove the oil from your skin and washing your clothes as soon as you can so you don’t transfer the oil to yourself, others or additional laundry is also a good idea. If your pets have been scampering about where PO could be present, give them a good bath before you snuggle up with them and consider wearing long rubber gloves like those made for doing dishes to avoid the oils transferring to you.

 

PO isn’t all bad; Black-tailed Deer, California Ground Squirrels and Western Gray Squirrels among other species consume the leaves of the plant which is rich in phosphorus, calcium and sulfur. Many birds eat the berries and utilize the plant for shelter. Research has shown that livestock, domestic dogs and other native wildlife species do not have adverse reactions to Urushiol. Native Americans cooked with it, used the stems to make baskets and used the juice from the fruit to dye materials black.

 

Don’t stay off the trail, just take precautions and enjoy winter hiking in your favorite monument! 


-Kristie Ehrhardt (kehrhardt@tuleyome.org)

Tuleyome Land Conservation Program Manager

RECENT ARTICLES

By Nate Lillge August 6, 2025
Bill Grabert is stepping down from his position as treasurer on Tuleyome’s volunteer Board of Directors – we thank him for his many years of service! Bill first joined Tuleyome as a staff member in 2016. His nature-based teaching influenced many youth over the years with school field trips throughout the Berryessa Snow Mountain National Monument region, from Redbud Trail to Conaway Ranch. As part of Tuleyome’s team of instructors for the California Certified Naturalist program, Bill inspired adults to care for the region. His love of the area began as soon as he graduated from college and began working as a geologist in Lake County. Bill has devoted his diverse knowledge and skillset to care for, steward, and enjoy California’s northern Inner Coast Range Mountains for many years. He will be missed on the Board but we look forward to seeing him on the trails! -Nate Lillge (Adventures and Engagement Director)  and Lyndsay Dawkins (Volunteer Tuleyome Board President)
By Bryan Pride August 6, 2025
Fifty-eight and a half million acres of America's wildest forests have been protected for nearly 25 years by the Roadless Rule, a conservation cornerstone that could soon disappear. Established in 2001, the Roadless Area Conservation Rule (RACR) , more commonly known as the Roadless Rule, designated "Inventoried Roadless Areas" (IRAs) across our nation's forests, prohibiting new roads from being built. Now, USDA Secretary Rollins wants to rescind it . From Alaska to California, the losses from this rollback would be massive. In Alaska, 92% of the Tongass National Forest could lose protection, threatening one of the world's most pristine ecosystems and the indigenous communities who call it home. California would lose protections across 4.4 million acres spanning 21 national forests , which has the potential to impact treasured places like Inyo, Shasta-Trinity, and the Berryessa Snow Mountain National Monument. Rule Born from Necessity, Not Ideology The Roadless Rule traces back to 1998, when U.S. Forest Service Chief Mike Dombeck saw the agency's vast road system as a major environmental and fiscal problem . To put this in perspective: the Forest Service maintains eight times more miles of road than the Interstate Highway System. The agency had too many roads to properly maintain for safety and environmental purposes, with poorly maintained roads contributing to erosion and other harms across national forests. The road maintenance backlog had ballooned to $8.4 billion while the agency received only 20% of the funding needed to maintain roads to environmental and safety standards. Dombeck proposed a moratorium on road construction in undeveloped forest areas across most of the National Forest System. The agency adopted an 18-month moratorium in February 1999 pending completion of an overall road management plan. Later that year, the agency undertook a rule making process to provide long-term administrative protection for roadless areas. The Forest Service conducted an extensive public involvement process that produced 1.7 million comments , with the majority favoring a strong national policy protecting roadless areas. The resulting Roadless Rule was not and is still not a blanket ban: it makes exceptions to allow access to non-federal land inholdings and pre-existing mineral leases, and allows logging to reduce fire risk, improve habitat or aid in the recovery of endangered species. What began as a fiscally prudent solution to an unwieldy road network became a cornerstone of forest conservation, one that Americans overwhelmingly supported then and continue to support today. The Administration's Claims vs. Reality According to USDA Secretary Rollins , the rule is “overly restrictive”, hinders fire prevention and responsible timber production, therefore the Rule poses “real harm to millions of acres of our national forests.” Rollins linked rescinding the Rule with Presidential Executive Order 14192, "Unleashing Prosperity Through Deregulation .” The reality is different. Rollins' claim ignores what's actually at stake. Roadless areas are essential ecosystems that provide clean air and water while keeping wilderness intact. They also serve as critical refuges for wildlife; 57% of America's most vulnerable species depend on roadless areas for habitat. For the 156 million Americans who visit national forests annually, these areas offer irreplaceable backcountry recreation experiences. Most strikingly, the administration's fire prevention argument is backwards. Scientific research reveals that 88% of wildfires are human-caused , and 95% of these fires start within half a mile of a road. Areas closest to roads experience 53% more fires than would occur by random chance. Less than 3% of wildfires start in wilderness areas more than a mile from roads. This research indicates that more roads through our forests are more likely to increase fires and would outweigh the effects of improving fire containment. While the administration claims roads improve fire response, fire management teams consistently identify inadequate resources and personnel shortages, not roads , as the primary barriers to effective wildfire management . Rather than building roads that increase fire risk, fire management experts advocate for investing in cultural and prescribed burns, fire mitigation and forest restoration, proven approaches that are underfunded but key to preventing future fires and reducing fire magnitude. What's Next? Rescinding the Roadless Rule will require a public comment period that has yet to be announced. This is when we can all share our views. Tuleyome will be following this issue closely and will be commenting. For more information on the Roadless Rule and how to participate in the public comment process or other advocacy opportunities, contact B ryan Pr ide .
By Kristie Ehrhardt August 6, 2025
The short answer is honestly, pretty much anywhere! Because the 344,476 acre Berryessa Snow Mountain National Monument (the Monument) is located in the rural areas of Colusa, Glenn, Lake, Mendocino, Napa, Solano and Yolo counties you will have a great view of the dark night sky, free from urban light pollution from virtually anywhere within its boundaries! The Monument is an easy drive from not only the metropolitan Sacramento area but also from the San Francisco Bay Area as well as the North Bay communities making it an easy day trip. If you’re here especially for the Perseid meteor shower though it might be a very long day since best viewing happens between the hours of midnight and early morning. If you’re adventurous and up for an all-nighter, be certain to pack plenty of water and snacks and be sure to pull over only where it is safe and you’re not blocking a road, especially when it’s dark. Also always keep safety in mind and look out for wildlife as the Monument is home to black bears, mountain lions, coyotes, tule elk and bobcats that may be traveling through the area as well. If you’d like to stay a night (or several), there are multiple developed campgrounds to choose from inside the Monument boundaries. If you’re up camping, check out The Blue Oaks Campground, Indian Valley Campground, Hunting Creek Campground, Deer Valley Campground, Lower Nye Campground, West Crocket Campground or Kowalski Camping area just to name a few of the sites available for overnight stays. Before you go though, please do check with the United States Forest Service or the Bureau of Land Management websites for details on the particular camping area you’re interested in as well as current conditions, requirements and fire restrictions. The Monument also offers primitive camping in the three wilderness areas located within the Monument boundaries. Cache Creek Wilderness, Cedar Roughs Wilderness and Snow Mountain Wilderness present nearly unlimited opportunities for dispersed camping or backcountry camping (areas located outside of designated campgrounds). Although camping is allowed and encouraged, these areas have no amenities such as tables, toilets, available water or waste removal and require you to pack out all trash and waste. There are no motorized vehicles allowed within Wilderness areas and they provide places for deep solitude with nature. Camping in Wilderness areas or other dispersed camping areas require visitors to understand and follow the Leave No Trace principles of outdoor recreating as well as planning ahead and knowing the area and what to pack. That said, other than the trees potentially blocking some of the night sky, you’re sure to avoid urban light pollution and have an unobstructed view of the night sky from practically anywhere within the Monument! -Kristie Ehrhardt ( kehrhardt@tuleyome.org ) Tuleyome Land Conservation Program Manager