It is a 1987 Kuwahara Cascade and really was designed more as an expedition bike than a mountain bike.
It has Ishiwata quad butted tubes, very slack frame angles, a long wheelbase, braze ons for multiple bottles and a seat pump, and even has a spoke holder for the rear stay.
I also have a Shasta that I converted to fixed that I ride in the winter and bomb around town on but it could handle some distances as well and has tires better suited for riding the trails. My Cascade was set up like this before I decided to make it a full on touring bike.
My favourite long distance bike, (and perhaps my all time favourite bike) is my 1955 Raleigh Lenton fixed gear... we have done many metrics and full centuries together in perfect comfort.