The Smith River National Recreation Area stretches along the river from Jedediah Smith Redwoods NP, nearly to the OR-CA border, and there's a nice little visitor center in Gasquet. There are a number of taxidermy birds and mammals, and interpretive displays on the geology, biology, climate and ecology of the region. The thing that most impressed me was the knowledge of the staff- or more accurately, their ability to put their hands on this or that pamphlet with details they didn't carry around in their heads. The center is no big deal, but it was a fun, quick stop. And I was pleased that they highlighted the unusual geology of the area.
Even if you choose to skip this stop, a feature to notice as you drive through town is the well-developed river terrace upon which the town is built. This is a nice, flat, well-drained surface for construction, and the Smith River has incised down into it far enough that I can't imagine flooding is ever an issue. I would guess the development of this particular terrace dates to the Pleistocene. Flying over the region to the Bay area, the higher peaks show lots of evidence of glaciation, which would have resulted in sedimentation in the lower reaches of stream valleys.