Checkered (or Common) White
A common white found nearly anywhere outside urban areas and most of the year. Much less common in suburban gardens than the Cabbage White, which thrives in gardens, while protodice uses a variety of native and non-native mustards. I've only seen them once or twice in my garden in Long Beach, but they do fly in open areas where there are wild mustards even within cities. In rural fields, they can be abundant. Females are more heavily patterned than males. I've found the caterpillars a few times on wild mustards - they use just about anything in that family. This is our native "common" white butterfly; Pieris rapae has taken that role in populated areas, but it's a relatively recent (1860s) migrant.