maybe white japanese roof flag iris?

It is one of the many species of beardless iris native to CA, known collectively as the Pacificas. I can't see it clearly enough to determine for sure but looks like either Iris purdyi or Iris chrysophylla, both of which can be found in the area you describe.

These native iris are the parentage behind the mixed Pacific Coast hybrids (PCI's), arguably the most attractive and fetching of any of the US native irises. And some of the trickiest to grow outside their natural range.

These links may help:

This one has a category of Calif. natives.
http://wiki.irises.org/bin/view/Spec/WebHome

And this one is the ultimate source of information and pictures.
http://www.signa.org/index.pl?Database

Thanks for all of the great info! I love the hybridized iris based on Pacific Coast iris - so fun to have found one of their ancestors! It is amazing how, if you grow something where they LIKE the climate, etc., the plants grow with no problems. There are also some species roses growing nearby the iris which are so happy they grow in large colonies right next to the road, and have even come up in the middle of the road right through the blacktop!

Right now the forest there is aglow with blooming wild dogwood, and I even found a stand of native wild rhododendrons. All, of course, growing with no help from humans whatever. Makes you wonder about all of the fussing we gardeners do...

Jackie

Siskiyou Iris, Shasta Iris and Yellowleaf Iris are common up here. Sometimes they crossbreed. This may be a Shasta Iris but it may also be a mix. I love it when they bloom!