There are lots of books about BC wild edibles. That book you mentioned is okay. This one is pretty good too, might be suitable since you're in the interior:
Food Plants of British Columbia Indians,
Part 2: Interior Peoples
http://www.amazon.com/Food-Plants-Br.../dp/B000K08ZX4
Here is another good one - actually more than good, it is excellent, I also have the companion book to it for the coast plants:
Plants of Southern Interior British Columbia and the Inland Northwest
http://www.amazon.com/Southern-Inter.../dp/1551052199
Also, this is a helpful website, it covers wild edible plants of British Columbia, Oregon, Washington, Montana, Idaho, the Rocky Mountains and Western Canada:
http://northernbushcraft.com/plants/index.htm
If you are ever vacationing and travelling on the ferries over to the island be sure check out the books section in the gift shops on the ferries. They always have a great assortment of illustrated books about BC plants including information about all the edibles and those to avoid. I've picked up some good books about BC plants, animals, marine life etc. on the ferries.
.
