The southern lower hills are mostly covered in grasslands and oak savanna. The northern rocky hills area is primarily chaparral shrubland and oak woodlands. The Simi Hills are part of the California chaparral and woodlands ecoregion. The oaks (Quercus spp.) include: the evergreen coastal live oak (Quercus agrifolia), the deciduous valley oak (Quercus lobata), and the scrub oak (Quercus dumosa). Riparian zone plants include California sycamores (Platanus racemosa) and arroyo willows (Salix lasiolepis). Spring wildflowers include the redbush monkey flower (Mimulus aurantiacus), Plummer's mariposa lily (Calochortus plummerae), and canyon sunflower (Encelia californica). poison oak (Toxicodendron diversilobum) is also an important member of the native plant habitat community here.