Our California state insect. In flight, males reveal a pinkish-purplish (structural) sheen in the poodle-head-shaped area outlined in black on the forewing. This area is yellow in southern dogfaces, which sometimes are found with this species (but are far less common here than in, for instance, Arizona). Female eurydice is easy to distinguish: they are basically all yellow. These two species can hybridize. They can both be quickly distinguished in the field from orange and Harford's sulphurs by their sharp wing tips. A black-edged hind wing usually means you're seeing a Southern Dogface male.
The larval food plants are false indigo, Amorpha fruticosa and A. californica, in the Fabaceae family. There are said to be two broods, though I'm not sure this is a hard-and-fast rule in the field. I've seen them from early January to late October. Females seem to like to place eggs where stems are beginning to form, and larvae eat the tender leaves.