1920 Geologic Map of Ohio, by John A. Bownocker. 32 x 40-inch format, scale 1 in. = 8 mi. (1:500,000). The 1920 geologic map was aided by complete topographic coverage for the entire state and was the most detailed to that point. It was the first to identify the Permian System in Ohio, and it identifies 14 geologic units and features a revised cross section of the state. This map was utilized by the Survey until the modern, digital map was released in 2006.