Can anyone identify this white flower for me?

Question

http://flickr.com/photos/kiragunderson/2686846819/

Answer 1

It looks like Romneya coulteri (Matilija poppy, California tree poppy). See these links for information and pictures:

http://images.search.yahoo.com/search/im...

http://www.laspilitas.com/plants/587.htm

http://www.wildscaping.com/plants/plantp...

Answer 2

You, my friend have opium poppies. good luck getting v&.

Answer 3

Your flower looks like a Lemon Chiffon Clematis.  You don't say how it grows, though.  Clematis are viny and climb a trellis or fence.