Pine White Butterfly

Update: Thanks Larry M. for the identification as a pine white!  You can find out more about it here.  They will need to change the "range" of this butterfly as I saw this one, and many others, on Whidbey Island.  This butterfly is now in northwest coastal forests.

Original post:
I tried to identify this butterfly online but the task is daunting.  Anyone know what this is?  I caught this a couple of weeks ago on the Maylor Point walk.