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Did You Know?

Oak trees have flowers, called catkins that grow into acorns when the miniature female flowers are pollinated by males. Trees bearing catkins are mostly wind pollinated, relying on wind to carry pollen to the female flowers so these trees must produce large amounts of pollen that can be seen as a yellow dust in the spring.

Valley oak catkin

Valley oaks can cross-pollinate with other oak species like the blue oak, resulting in trees that are hybrids of each variety.

Acorns fall from oaks to the ground and sprout roots that grow into seedlings under the right conditions.

oak seedling

Home for Bees

Bees create hives in the wild, inside a variety of tree species including oaks.

The Biggest Valley Oak

The "Henley Oak", in Covelo, California, is the tallest known North American oak, reportedly standing at approximately 150 feet. After 500 years or more, the valley oak has grown into the largest valley oak in the United States.

The Henley tree's base is so big it would take 20 people standing shoulder to shoulder to encircle it.

The Henley Oak

image credit: Denison Design

Valley Oaks

Valley oak tree at Lagoon Valley

Quercus lobata, also called valley oak, is the largest of the North American oaks. It is a deciduous tree, shedding all leaves in the fall. Valley oaks are endemic to California, meaning they are native to this specific region of the world. Valley oak trees may live for up to 600 years, so some trees we see today may have been living with indigenous people in this area, long before Columbus came.

Identification

The bark of the valley oak sort of looks like alligator skin, and the branches of large trees often curl and wind toward the ground. The leaves are dull and have lobes that start near the stem.

Valley oak leaves during various seasonsThe truck of a mature tree can grow to be 6-10 feet in diameter, with a height of 100 feet.

Importance to Wildlife

Valley oaks can commonly be found in oak woodlands and riparian forests adjacent to rivers or streams.

Remaining valley oak riparian and woodland areas comprise critical habitat for wildlife including nesting bird species and several endangered species in California.

bird nest cavity in oak tree

Valley oaks are used by various cavity-nesting and cavity-storing birds and mammals.  Black-tailed deer, various rodents, gophers, California ground squirrels, and deer mouse eat valley oak seedlings.

Acorns are an important diet item of the California ground squirrel, pocket gopher, scrub jay, yellow-billed magpie, acorn woodpecker, black-tailed deer, feral pigs, and cattle.  

green acorns in child hand

Range

Valley oaks are only native to California and can be found in Central California, northern central and coastal inlands. 

Range of valley oaks in Central California to western coast regions

Growth

valley oak tree

Valley oaks grow quickly, reaching 20 feet in 5 years, and 40 feet in 10 years. 

A tree is made of cells, and more cells are added each year. The cambium layer just beneath the bark adds cells to both the tree tips and the outside of the trunk and branches, so each year’s growth makes the tree both taller and thicker. 

Trees grow faster during wet, warm seasons and go into dormancy in cold, darker or dryer seasons. The wood structure and appearance respond to these changes, so when we look at a piece of wood (the top of a stump or the end of a board) we often see ring-like patterns called “growth rings.” 

The cambium cell layer is the growing part of the trunk. It annually produces new bark and new wood in response to hormones that pass down through the phloem with food from the leaves. These hormones, called “auxins”, stimulate growth in cells.

cross section of a tree

Indigenous Use of Acorns

For thousands of years, acorns produced in the oak woodlands were one of the most important food sources for the indigenous people. 

acorns

While very bitter in their natural state, once ground, leached and cooked, acorns were an excellent accom­paniment to other native foods such as venison, salmon, or berries.

Pena Adobe sits next to Lagoon Valley, which was once a marshland prior to the creation of the 80-acre, man-made lake. Long ago the Southern Patwin Village of Malacca was on the north side of the marsh. Grinding stones were used to grind acorns with hand-held stones. Over time, holes were bore into the stone slabs. Many historical and sacred indigenous sites are now being protected across Solano County by organizations like Solano Land Trust in partnership with the Yoche Dehe Wintun Nation.

grinding stone at Pena Adobe