Eagle Creek valley clay under an 1852 rail town
Zionsville was platted in 1852 in the Eagle Creek valley in southeastern Boone County, and homes near that low-lying original townsite sit on the same expansive, clay-heavy glacial till found across Hamilton and Boone County — soil that absorbs water and swells, then shrinks and cracks as it dries, putting cyclical pressure on foundation walls.
Older foundations and modern backfill don't behave the same
Foundations dug for Zionsville's historic Village-core homes were backfilled decades before modern compaction standards existed, and that loosely packed soil holds water longer than undisturbed native ground, driving much of the settlement and cracking seen in the older part of town.