Valley oaks (Quercus lobata) reach the southernmost extension of their range in Malibu Creek State Park. Endemic to California, valley oaks were once widely distributed from the Sacramento River delta, 500 miles south to the Santa Monica Mountains. These trees, which reach truly majestic proportions, originally spread over the native grasslands in the wide valleys of central and coastal California. Valley oaks reach ages of 400-600 years and may have trunks six to seven feet in diameter. They present a graceful appearance on the landscape, widely spaced with branches that may drape to the ground.
Over the last 150 years, valley oaks have succumbed to widespread agricultural and residential development that has focused on their prime habitat - alluvial valleys. Although thousands of acres of valley oak savanna remain, they are vastly changed. The savanna or grassland understory was formerly comprised of dozens of species of native grasses and forbs, which blossomed in an array of wildflowers in the spring. Now the grassland understory is comprised mainly of non-native annual grasses, which have out-competed and crowded out the native species over the decades since they were introduced.
Where once a multi-layered composition of valley oaks of different ages existed, now only large trees remain. Many years of non-seedling growth have resulted in low replenishment of young or medium aged trees to the valley oak savanna.
Aside from valley oaks, characteristic native grasses, which dominate valley oak savanna, include purple needlegrass (Nassella pulchra), and non-native grasses such as wild oats (Avena fatua) and ripgut brome (Bromus diandrus), as well as black mustard (Brassica nigra). Wildflowers include mariposa lilies (Calochortus catalinaea) and coast goldfields (Lasthenia chrysotoma).