You can read about use of Garry Oak acorns by Northwest Coast tribes here (it's a PDF download, the first article is the one). This has been seriously underestimated by archaeologists but evidence is mounting that acorns were an important supplement to the diet in this area, even though they required extensive processing (leaching) to make them edible.

The reference is, if you don't want to download it:

Bethany Mathews 2009.

Balanophagy in the Pacific Northwest: The Acorn Leaching Pits at the Sunken Village Wetsite and Comparative Ethnographic Acorn Use.

Journal of Northwest Anthropology Volume 43 (2): 125 –140.

Hopewell communities were making acorn flour with complex processing to remove bitter tannins 2,000 years ago.