Reading the original Wizard of Oz I am a little confused by the origins of the road.

It seems to pre-date Oz arriving, as people discuss their people going to the emerald city long ago. It also seems poorly maintained with bridges missing or holes in.

Building a road, especially one of yellow bricks seems like quite a difficult undertaking, so who did it?

It seems like there is not great continuity in the Oz books, is this discussed in any of them?

Note: I would prefer information from the original Baum books.