Matilija Poppy
Papaveraceae (Poppy Family)
Romneya coulteri Harvey

More about the Matilija Poppy (with photos) here:

http://www.calflora.net/bloomingplants/matilijapoppy.html

also, more here:

http://www.laspilitas.com/plants/587.htm

Matilija poppy is a glabrous, shrubby perennial, heavy branched and woody at the base, growing to 8' tall. The showy white flowers are the largest of any plant native to California, and look like fried eggs. There are 5-8 per stem and the six petals are usually crinkled with many yellow stamens and a single large pistil. The three sepals are glabrous, which differentiates it from the other Romneya species, trichocalyx, which has bristly or appressed-hairy sepals. The leaves are alternate and have 3-5 main segments which are somewhat dentate or cleft. Matilija poppy inhabits dry washes and canyons below 4000' in coastal sage scrub and chaparral away from the immediate coast. It is an occasional resident in the Peninsular Ranges, but is more common in the Santa Ana Mts to San Diego Co., being found also in the Santa Monica Mts where it was probably begun by transplanting. It blooms from May to July. The name Matilija appears to be of Chumash origin, and there is a Matilija Canyon above the community of Ojai and a Matilija Creek in the Los Padres National Forest.