As my brain is wont to do, it immediately began to imagine the Multinomah visitor center as something other than a roadside tourist trap. What if the visitor center was actually a roadside stop along some trade route? It makes sense that travel back in the day would be governed by a couple of related factors. 1.) The distance someone could travel in a day 2.) The presence / location of survival resources and 3.) The presence of navigation landmarks. Multnomah falls reimagined could easily fit one or all of these requirements for a regular rest stop along an overland trade route.
I imagine the fictional house at Fallside arose as traffic expanded a common camp site into something more permanent. The house served as a place to rest, share news and conduct a little business. Perhaps local woodsmen sold game to resupply merchant caravans with meat or foraged goods. Woodcutters might do the same with firewood. Perhaps the builders of the house set up a cave in the cliff near the falls for aging local brews. If the house was located at one end of a particularly difficult stretch of road, such as a mountain pass, it could also act as a place to pick up expert guides or hired muscle.
I actually have a couple other map ideas for Fallside, including an exterior map of the surroundings and one for the cellars beneath the house. Those, however, will have to wait for another Monday.