I have started actively researching the natives who lived in Cascadia before whites came to this region. I want to understand how people used to live here, how they used to feed and house and clothe themselves; whether and when they migrated to temporary camps or stayed in permanent dwellings; whether and why they developed rank/hierarchical societies; and any other patterns which might influence the direction of my own tribe as we choose where and how to live. At this point, I have only read a little bit about natives in the area, so I'll just post here about resources I've found helpful or which seem promising.
Nancy Turner: much of her work focuses explicitly on issues of food and plant technology of first peoples in this region. I especially recommend Keeping It Living (examination of plant culvitation strategies of first peoples), Plant Technology of First Peoples in British Columbia, and her four-book Edible Wild Plants of Canada series with Adam Szczawinski (covering Wild Coffee & Tea Substitutes, Wild Green Vegetables of Canada, Edible Garden Weeds of Canada, and Edible wild fruits and nuts of Canada; her more recent Food Plants of Interior First Peoples and Food Plants of Coastal First Peoples cover much the same information, but didn't seem quite as in-depth and detailed when I spent some time flipping through the older vs the newer series). I also have her book Common Poisonous Plants and Mushrooms of North America (also coauthored with Adam Szczawinski), but I really haven't used it enough yet to recommend it or not.
Native American Ethnobotany: This book by Daniel Moerman gives encyclopedic information on plants used in different ways by different tribes. To learn how local tribes lived, you can look up the tribe in the appropriate section and browse through all the known uses of plants as drugs (for example: Burn Dressing, Love Medicine, or Venereal Aid), food, fiber, dye, etc. This book does not give much detail on how the plants were used, so you'll usually have to go to the referenced original source to see more information on how to process a plant.
Erna Gunther: wrote Ethnobotany of Western Washington, which I checked out from the library a while back and found interesting but haven't added to my own library yet. I don't have it here but I think it focused on coastal tribes (Gunther worked primarily with the Salish and Makah people.)
General pre-history & archaeology: I read The Prehistory of the Northwest Coast, by R. G. Matson and Gary Coupland, which gave me some good information mixed in with way too much detailed archaeological blow-by-blow history for what I needed. I skimmed over the archaeological details with eyes glazed, perking up for the summary bits or other interesting notes which jumped out at me. Also, when the book says "Northwest Coast", it means west of the coast range, not including the interior areas like the Willamette Valley, about which I feel most curious. I don't recommend this book unless you really want the archaeological stuff.
I've read halfway through a similar book, Peoples of the Northwest Coast: Their Archaeology and Prehistory. This one spends two chapters on much the same archaeological material but also spends eight chapters on theories and conclusions regarding how people actually lived. This book also covers only west of the coast range. I do recommend this one for info on coastal living.
So far I've only found one book specifically covering the Willamette and Umpqua Valleys: The World of the Kalapuya: A Native People of Western Oregon, by Judy Rycraft Juntunen, May D. Dasch, and Ann Bennett Rogers. Since I live in this area, I find this book particularly exciting! And since I don't expect my tribe to live on the coast, I find the information about inland first peoples more useful than that about those on the coast. I do wish the book would go into more detail on its subjects; the authors wrote 117 pages covering a wide range of topics, touching on many of them only lightly. Juntunen originally gathered information to provide to teachers and students. Although the authors rewrote much of the text to target a more general audience including adults, it still reads like a middle- or high-school book. It doesn't give botanical names for any of the plants mentioned, and warns twice: "Do not attempt to ingest any Willamette Valley native plant." Despite the somewhat simplified text and coverage, this book gives information I haven't found anywhere else yet, so I highly recommend it for this specific area!
Cultural Resource Overviews: I just discovered these! Apparently the US Forest Service released many volumes in the late 1970s into 1980s exploring the prehistory and history of different national forest areas. The volumes don't focus exclusively on first peoples, as they include recent white history, but they seem well enough organized that I can easily skip the parts about which I don't care. So far I've found mention of volumes covering the Siuslaw National Forest, Willamette National Forest, Siskiyou National Forest, BLM Lands in North-Central, northwestern, west central, and Lakeview District south-central Oregon (I don't know exactly which ares those BLM volumes cover). The Siuaslaw book through which I flipped had great detail on how natives lived. If they all provide the same level of detail they should help a lot in understanding lifestyles of micro-regions in this area.
Two broad-region resources I haven't read or used yet, but which look useful: A Guide to the Indian Tribes of the Pacific Northwest, by Robert H. Ruby and John A. Brown, and Handbook of North American Indians Volume 7 Northwest Coast, edited by Wayne Suttles. Ruby & Brown's book gives short (one to a few pages) summaries of prehistory, history and current status (as of 1986) of many different tribes east and west of the Cascades. I notice that it has no entry for the Kalapuya, though it does mention them under other entries (for example the Molala and the Confederated Tribes of the Grand Ronde Community of Oregon). This definitely doesn't give great detail on individual tribes, but seems a helpful resource for a quick overview. Suttles' book covers primarily the coast, but has a chapter on the Chinook, one on "Prehistory of the Lower Columbia and Willamette Valley", and one on the Takelma also in the interior. The first part of the book covers general subjects of History of Research and History of Contact, before a few dozen chapters on specific tribes or regions.