In photos elsewhere it looked kinda like a Unimog to me, but I'm not sure.
I don't know where the family was from, but those of us who come from wetter places in the eastern US don't always realize how dangerous streams in the West can be. A stream ford that's dry most of the year can become a raging torrent after a thunderstorm. I'd never even seen a road that forded a stream until I moved to SoCal (other than unmarked logging roads.)
1990 E-250 Sportsmobile w/ penthouse top, converted when new by SMB Texas.