In contrast, its growing season can be 20 days longer than that of the Highplains subsection to the west. Average annual precipitation is 28 to 30 inches, and annual snowfall is 40 to 60 inches, increasing at the inland margin of the subsection. Pennsylvanian bedrock consists of sandstone, shale, coal, and limestone.
Mississippian bedrock is primarily limestone and gypsum.
Lake plain characterizes Sub-subsection VII.1.1. A major delta is located at the mouth of the Au Sable River. Sub-subsection VII.1.2 is primarily ground moraine and end moraine. Most of the few lakes in the subsection are concentrated within small areas of end moraine and ice-contact topography. Several large rivers are concentrated on the sand lake plain.