A few years back, an otherwise fit and competent loop hiker and climber type tried to exit the "ptarmigan traverse" in washington by walking down a drainage eastward and trying to link up with a mapped valley bottom side trail branching from the Pacific Crest Trail. Whatever trail may have existed was gone, and he spent the better part of the day traveling about a half mile an hour and exfiltrating out to the PCT at dark. Beaver dams, swamp, 8ft devil's club, alder, nightmare. This was on the drier "east" side of the cascade divide.
Folks who've been dumb enough to shoot something on the far side of such a creek bottom, or want to climb a peak in the neighborhood, spend as little time as possible in these places, crossing the creeks at right angles and climbing to open forest or treeline.
I'm not sure anyone who's not been there, can comprehend just how thick/impenetrable these places are. And they are everywhere. Now project that northward along the BC coast range. Limitless, untouched and unseen country.
The historical incentive to explore these places was gold prospecting, and it's likely that a lot of these creeks were walked on nearly their entire length. It's not as if there's a lack of "stories" about bigfoot from that time period.
