Briny, I love using native plants and your area would be a lovely spot for that. Here's some ideas, and I've tried to use my own photos since I am close to you in location. If you open each photo, it will bring you to the main database and you can see other photos as well.
False lily-of-the-valley. This is a shade loving ground cover that once introduced will colonize rapidly where conditions are good for it. I first discovered this when moving some forest dirt up into my beds as mulch. I soon got this pretty little plant growing in all my shady locations. It carpets the ground lushly, blooms in early spring and dies back by midsummer or so. Also known as snakeberry.
Deer fern. A delicate fern that stays fairly low.
Sword fern. Some folks are leery of this because they can get quite large. I love them as an understory to evergreens. They are evergreen as well, but near my yard I cut the old fronds to the ground in late winter when the new one start poking out to tidy them up a bit.
Vine maple. A good addition in dappled shade - near the edges of your evergreens. Will mature at about 20'. Gorgeous fall color.
Kinnikinnik. Another ground cover, but this one wants more sun. It is evergreen and would be a good choice between your native area and lawn (if you intend to have one). It colonizes quickly, has pretty pink flowers, and later berries.
Devil's club. This would be an adventurous addition to the far side of your creek. It is quite an impressive plant, but definitely packs a sting! It will also colonize and does well with ferns.
Western azalea. I absolute love this plant - more delicate than its cultivar cousins. I unfortunately lost all 5 of mine last winter, not sure why (they may have been in too exposed of a location).
Red flowering currant. Another stunner. Blooms in spring, and very easy to propogate (just but off some end sprigs, dip in hormone rooting compound if you want, stick in a pot of dirt, keep well watered and plant out in a year or two). This likes full sun.
Indian plum. Grows at the edge of the forest, makes a great summer screen. One of the very first plants to break dormancy for me and has early white blooms, followed by tiny dark plums that the birds love. I am encouraging these to colonize in an aspen grove between us and the neighbor in this photo.
You could also open my personal plant list and limit it to the category of 'native' for some other ideas.
http://garden.org/lists/view/B...
Good resources I reference often:
Native Plant Association:
http://www.wnps.org/
King County Native Plants:
https://green2.kingcounty.gov/...
Have a wonderful time with your project, and please keep us updated with photos! I grew up in Lake City and know your area well, beautiful setting.
