No scale on this one, but the larger pebbles are about an inch and a half or two in their longer dimensions. I think we're in Lookingglass formation here, but I'm not positive. Lookingglass is the precursor to the Tyee formation, which utterly dominates the Oregon Coast Range. The former is derived from erosion of Klamath Mountain bedrock, while the latter was derived from a much larger area of predominantly granitic rock farther to the east- probably the Idaho batholith or something similar. The general story I've come to understand is that the same drainage/river system carried both generations of sediment, but that river likely captured another and its sediment load, which overwhelmed the Klamath-derived sediment.