Yes its at miami woods, at the corner of oakton and caldwell, there are two entrances to the preserve. One on caldwell and one on oakton. Enter on Caldwell cuz IIRC they are two different sections.
http://www.geocities.com/chicago240sx2003/mqmapgend.JPG
Go there you might have to copy link and paste in new window (geocities sucks).
And yes its the 20th saturday, get there around noon.