Ron Garret wrote:

The assigned route was not on an airway, and so there is no minimum IFR
altitude on the route.

Not so. If you're off an airway, then the off-route obstacle
clearance altitude (OROCA) applies, and is printed on the LO charts.

The first 250 miles or so are over pretty flat terrain. It is only
shortly before you get to the destination that the mountains begin.

Lost comm minimum altitudes apply per segment, not per leg. So in
this case, you would need to climb when you enter the grid square
containing tall rocks.

- FChE