Oaks are one of the most common trees that grow in rural parts of Northern California. California oaks can vary greatly in appearance, making identification of oak trees more difficult. For example, coast live oaks are tall trees with shiny, prickly leaves, while leather oaks look like shrubs with fuzzy leaves. According to the Hastings Field Station of the University of California, identification of oak trees can be made more challenging because two species of oak may produce an intermediate hybrid that does not have many of the characteristics associated with oak trees. Carefully exam a tree to determine if it is an oak.
Examine the branch of your tree. While oaks such as the scrub oak produce leaves that do not resemble traditional oak leaves, all oak plants produce leaves that are arranged spirally on the tree.
Look for long, hairy, string-like flowers. These flowers, which are called catkins, are produced in the springtime on oak trees and shrubs.
Examine the oak tree nut, called an acorn. An acorn is a brown, oval nut held in a cup-like cap. Oak trees begin to produce acorns after they have matured 20 years. Since young oaks do not produce acorns, absence of an acorn does not necessarily mean that a tree is not an oak. But the presence of acorns is a definite sign that the tree is an oak tree.