That explains some things. I've wondered why they didn't dig up the asphalt as well.

That has to be a different monster to tame as far as track prep goes.

During the 80s Avilla was also dirt on top of asphalt and as I remember could be quite unpredictable. Despite that, it also produced some great inside/outside Hoosier bullring battles.

Walking in to Plymouth and later watching Robert Ballou swoop outside of traffic through turns 1 & 2 it reminded me a lot of Avilla.

(Side note: Robert didn't care for the surface as anyone that was there that night might remember.)