Oak Park is a narrow riparian band with sycamores, live oaks, and eucalyptus.  It is fairly open and can easily be birded in 30 minutes.  It is popular on weekends and sometimes there are large festivals.  The best birding is along the creek.  There is access on both sides,  make sure to check all eucalyptus as the fall migrants usually end up there.  There is a hige stand of Eucs by the Tennis court picnic area which usually holds most of the migrants in the park.  Rarities include Northern Parula, American Redstart, Magnolia Warbler, Summer Tanager.  Otherwise, the park holds regular residents such as Oak Titmous, Hutton's Vireo, Bushtit, Anna's Hummingbird, Nuttalls Woodpecker. Winter can be good for finches. Spring migrants can sometimes be seen flying over head, but they rarely linger long in the park.