Geologist here! I'm a fan of this project. The maps are only part of it; they're trying to build a three-dimensional scaffolding (based on drill cores, etc.).

Almost all normal geologic maps are maps of the rocks at the surface, since that's what we can see most easily -- but the rocks are no less complicated with depth, and in principle with enough data you could make the same sorts of map at any depth within the crust.

The same team is also working on data-mining from (academic paper) PDFs - some of the information from which may eventually be tied into the Macrostrat framework: https://geodeepdive.org/