My guess is that it was a creek that was buried. The practice was incredibly common in the 1860s and numerous developments over the years likely redirected or cut off the source further upstream. Seeing how Alton has few tributaries unlike East Alton and the towns past Fairview, this is a plausible explanation. Toronto, Seoul, London, Bangkok and Calgary all have plenty of buried creeks, may of which city planners are either rediscovering as they look to ease flooding or are uncovering in acts of beautification.