The vast state of California incorporates USDA hardiness zones 5a to 11 but the majority of the state, the central section excluding borders, is in zone 9. Finding hardy drought-tolerant plants for the majority of California isn't difficult. These plants will be able to withstand a couple of months between rainfall without additional watering.
Japanese laurel (Aucuba japonica) is from the dogwood family and is an evergreen shrub that is drought tolerant. It gets to 8 to 10 feet tall with 8-inch leathery leaves. Flowers are purple on male plants and red berries are on female plants. Plant this one in light to deep shade. Propagate via stem cuttings, seed or semi-ripe cuttings and grow in USDA hardiness zones 6 to 10.
Oxeye sunflower (Heliopsis helianthoides) is from the aster/daisy family and is an easy-to-grow perennial that is drought tolerant and attractive to butterflies. It will get 5 feet tall with dark green leaves 3 to 6 inches long and rough textured. Flowers are from summer to fall in yellow or orange 2 inches wide. Plant an oxeye sunflower in fertile soil with good drainage in full sun or light shade. Propagate via seed, division or cuttings and grow in USDA hardiness zones 2 to 9.
Angel's trumpet (Datura inoxia var. quinquecuspida) is from the nightshade family and is a fragrant, drought-tolerant perennial shrub. It gets 3 feet tall and twice as wide with trumpet-like flowers in white or lavender and 8 inches long. Coarse leaves are 10 inches long and smell bad. Plant an angel's trumpet in partial sun or full sun in well-drained soil. Propagate via division of roots and seeds and grow in the USDA hardiness zones 5 to 10.
Lion's ear (Leonotis nepetifolia) is from the mint family and is a hummingbird-attracting annual that is drought tolerant. It gets 8 feet tall with smooth leaves 2 to 5 inches long and clustered tubular flowers 2 to 4 inches wide. Plant this one in full sun or intermittent shade with regular watering. Propagate via seed and grow in USDA hardiness zones 8 to 11.
Nellie Stevens holly
The Nellie Stevens holly (Ilex x "Nellie R. Stevens") is an evergreen shrub that is drought tolerant and attractive to songbirds. It gets 15 to 25 feet tall with thick leaves and is full of red berries. Plant this one in good sun in acidic, moist soil. Propagate via cuttings and grow it in USDA hardiness zones 6 to 9.