Mystery Plant No. 5

I am looking for help identifying another mystery plant that came up in the garden.  This one is growing behind the west garden at the edge of the property in a terrible, dry, rocky, dusty spot.  It has received no help from me, so it must be quite hardy.  It is growing in total shade and competes with blackberries and Oregon Grape.  I don't know if it is a native, something introduced or an escapee from someone's garden.

When I spotted the plant, my first thought was Geranium or Crane's Bill.  I did an image search, but found nothing quite like this one.  Some members of the Aster family also have finely divided leaves like these, but again, no match found.  Here is a closer look at the leaves and the whole plant:


The photos were taken today, July 1, so we can say it is a July bloomer here.  There are several more clusters of flower buds along the stem.  The flowers are 2 in/5 cm across and this plant is 34 in/86 cm tall.  So far, I have had good luck getting ID help from friends on the internet.  Perhaps someone will know what this one is as well.

Past mysteries solved:

Palmate Coltsfoot  (Thanks Mike B. at Slugyard)

Japanese Photinia  (Thanks Roman Soroka in Australia)

Purple Toadflax  (Thanks Malcolm in the U.K.)

Cherry Plum  (I got this one myself)