Right you are.
WW I was still in living memory as was the depression and WW II. As you say, a lot of living in those people at the time. Writing about life on the frontier was a natural for them.
Plus, the frontier had closed only 60 years before 1950, so frontier life was still in living memory as well.
Even boomers knew a lot of people born in the 1800s, and an example of how current the West was to 1950s adults in Hollywood would be Wyatt Earp who died in 1929.
Hugh O’Brian was almost 4 when Earp died and would be playing him on TV 26 years after Earp’s death.
My own son probably sat in the lap of some people born in the 1800s.