Oak Leaves Across the creek from the Arboretum Headquarters, a line of large old Valley oaks towers over an open underplanting of toyon, California coffeeberry, elderberry, California hibiscus, red-osier dogwood and others. This makes up the Valley Oak Grove. Bigleaf maples grow along the path here and a planting of tule, rushes, and arroyo willow at the edge of the creek provides teaching materials for classes studying learning about the traditional uses of native plants. A large California sycamore dominates the west end of the collection and at the east end, a planting of island mountain mahogany forms an understory for a grove of coast live oak.