The junk piles represent the ruins of previous settlements or towns. I don't think there are near term plans for visible ruins of buildings, bridges or other structures. The roads in game are fairly close in placement to some of the real life roads around the Tahoe area.
later after prelude these areas are supposed to open up for expanded gameplay. once the mist starts receding whole cities will open up, being dangerous areas as well i would assume with everything alive warped by the mist.