Photo: Diane Edwardson, March 14, 2015. This appears to be a Painted Lady Butterfly (Vanessa cardui) as opposed to a West Coast Lady (Vanessa annabella). (Click on photo to enlarge.)
Of course, the butterflies were super active above the historic viaduct footings again yesterday. I could not get a clear shot of the other side of its wings, which are quite boldly patterned.