It's hard to get angry at Stinky Bob, even as pernicious as it can be at times. It is such a lovely little plant, and its flower has such a charming little face...but don't be fooled - it is a Class B weed and should be controlled as much as possible. The general idea is to get after it before that pretty face changes into the seed pod. It is pretty easy to get out of the ground after a good rain...but like a lot of nasty weeds, it has the habit of breaking off just above the root line if its feet are well-planted in dried dirt. Below is a shot of pretty much an entire plant, roughly 18"worth of it from tip to tap.
It's proper name is Geranium Robertianum (Syn.Robertiella robertiana), but like many another miscreant, it has many aliases: Death Come Quickly, Red Robin, Storksbill, and Crow Foot. But be careful when you go after it, especially during this time of the year, because the smaller ones can easily be mistaken for native Pacific Bleeding Heart. The two like the same habitat, and Stinky Bob can completely wipe out a stand of our lovely little native plants in a single season.