This is not a great photo, but the fly is so camera shy that I probably won't get a better one. It's a bristly
Tachinid Fly (
Tachinidae in the order
Diptera) working new composite flowers of
Palmer's Goldenbush (
Ericameria palmeri var.
pachylepis) growing on the dry flood plain by the river. The distinctive fly has whitish "windows" on its abdomen. I've seen the same flies lately on composite flowers of
Coyote Bush (
Baccharis pilularis) and
Bush Groundsel (
Senecio douglasii) shrubs. (Paradise, Santa Ynez River, 10 November 2009)
Checking at BugGuide, this fly might be in the genus
Peleteria. See
http://bugguide.net/node/view/53639.