There were, however, places here and there where the existing wood did not get replaced ... not back in the 1880's and not up till the present. One alley was like that up where we lived when I was a kid (it's the alley just north of Fullerton that starts at the alley a half a block west of Clark ... the main wood area then was at the "T" where the alleys met), while most of them were brick, and some had had modern cement/blacktop resurfacing.
I had forgotten about one alley down by us that was also this way. These shots are from the alley a half block south of North, from State to Astor, right behind the Cardinal's mansion. Since the area up there is (or was up until the 1970's when some highrises came in) all mansions, the traffic volume was not much, so this stretch of "wood street" is pretty well preserved.
I really don't know the details on these streets/alleys, but I assume that they were made with thick stakes pounded into the ground, as I can't imagine that if they were just blocks that they would have lasted this long. As you can see from these pics, they're not of a uniform size, but they seem to be around 4x6" in general. As is evident from the bottom of the detail shot, they even made some effort to "match" the wood, which makes me think that they cut the lumber on-site from logs.
Anyway, this is one of those "cool things about Chicago" that I don't think even a lot of Chicagoans know about, and I'd been wanting to get pics of it for a long time. We'd gone up to the park on Saturday, and came back via a different route than usual, and I had my camera, so when we passed this, I got these. Thought I'd share!