The unique physiography of the region can be seen in the hillshade view presented on Index Map A. The landscape is dotted with lakes that are incised into the surrounding sand hills. Large, flat bottom prairies, such as Levys Prairie in the southwest section of the Interlachen Sand Hills, attest to the erosional process of internal drainage into sinkholes. There is only a poorly developed surface water drainage system in the sand hills. A well developed drainage can be seen in the northeast section of Index Map A in the Penny Farms Uplands. This is related to the thicker section of Hawthorn Group and the lack of sinkhole development.

The irregular shape of Lake Johnson gives it a perimeter of over 10 km, with an area of only 2 km². Lake level at the time of the survey was 29 m (95 ft) NGVD. Gold Head Branch flows into Lake Johnson from the northwest and there is no surface water outflow points.