Medium-sized, dark-rumped storm-petrel with a long, deeply notched tail and grayish tones to the plumage. Usually flies fairly directly with light fluttering wingbeats; can be stronger in windy conditions. Look for pale stripe on underwing (not always obvious). Distinctive within limited range, exclusively off California and northern Baja. Rarely seen from land. Gathers in large flocks, often resting together on the water; can be mixed with other storm-petrel species.