Finding the identity of this weed proved to be a little problematic.
I have a wonderful book that I use for weed identification, it is called 'Weeds of California and Other Western States' and is published by the University of California, Agriculture and Natural Resources (ANR). (If anyone is interested, it is Publication 3488.) The book is actually two volumes; Vol. 1 covers Aizoaceae - Fabaceae and Vol. 2 covers Geraniaceae - Zygophyllaceae. All fabulous stuff, but although extensive in its coverage of California weeds it would be impossible for a single reference book to include every weed - as is the case with my weed of the day, purple sanicle (Sanicula bipinnatifidia). A member of the same family as parsley, purple sanicle is native to the west coast of North America so it surprises me that it was overlooked in the ANR book.
I just love this little weed, whose deep-red orbs just seem to float above all the other surrounding vegetation. It is a rather elusive weed and only grows in one area of Vinoland. Yes, again, that would be on the slope above the house.