A celebration of California Oak Day will be held Sunday afternoon at Topanga State Park.
Topanga resident Rosi Dagit, a certified arborist and author of a children's book about an old oak, said the day is held to recognize oaks, which are "losing a battle to development and lack of regeneration."
To help with that battle, volunteers will gather and plant acorns in hopes of keeping the forest alive.
Participants will have the opportunity to take a short hike over to the "Grandmother Oak," a 240-year-old park favorite.
The tree is big enough for some children to fit within its hollow trunk and climb up and out through a branch hole.
The Grandmother Oak has lived through the days of the Gabrieleno and the Spanish rancheros and on through the present, Dagit said.