I have several forestry maps of the area and all of the roads have names or forestry road number like 9S07 some of which Basecamp defines as "undxx" so makes me think its peculiar to Basecamp. The particular road Und35 shown on Basecamp does not exist in the forestry maps but the forestry map shows a mine, Maple Load Mine, near the terminus of Basecamps Und35. So again, undeveloped makes sense. I suspect an old abandoned mine road. Ill check it out on friday
"Und" means "undeveloped road". It's the name of the road/path in the map.
It has nothing to do with Basecamp.
Und term must be peculiar to Basecamp.