Here is the website that I used to find the 1930 aerial picture of the intersection of Kimberly and Brady seen in the previous post.
Iowa DNR Interactive Map
It works mostly the same way as Google Maps or Mapquest, or even more similarly, the Davenport GIS system that I linked to a while back.
In order to find an old aerial picture of an area, just zoom in on the area, and then over on the left hand side, scroll down to the bottom, check the box for the year you want to see, and uncheck the box for "Air Photography (CIR) 2002." Then click the "Redraw the Map" button and the map will then update with whatever version was chosen. Some of the areas have better photos than others, but overall its a fun tool to play with.
Here's an image of the website, with the area surrounding Vander Veer selected, in 1930. You can see that there was still plenty of farmland south of Duck Creek in those days.