The coastal mountains are young mountains. They are still growing. The highest and most imposing of the coastal mountains are the volcanoes. There are many active or recently active volcanoes dotting this coast. The tall mountains along the coast are often snow-covered year round.
Snow cover is important for the salmon.
As it melts in the summer, the run-off flows into the streams and swells them, raising the water level so the salmon can begin to swim inland. Sometimes even the snow melt doesn't make the rivers deep enough. Then the salmon must wait for additional rain in the summer to swell the rivers so that they may return to their home streams.