this is the location Trillium 'Del Norte' is supposed to be found.
as seen from the road

click on thumbnail for larger image

 closer look

April 2, 2008
seems to be a good mix

they look similar but different from the other Trillium rivale
I have found at 2 other locations

here is a pict of the Trillium from SF2.75

 here is a pict of Trillium rivale from location SF11.2