This is Becker's White nectaring on host Bladderpod at Yaqui Well in Anza-Borrego Desert State Park, January 17, 2006.
Those that emerge early in the year are more darkly marked. (This date was an early record for California.)

Another early dark Becker's White, this one a female from Sentenac Canyon in Anza-Borrego Desert State Park, March 1, 2009.

A male Becker's White, Yaqui Well, October 11, 2005. Males are more lightly marked than females dorsally.

Another male Becker's White at Yaqui Well on the same day as the male above.

A female from Yaqui Well. February 11, 2008.