Geologic units in Chisago county, Minnesota

Middle and Upper Cambrian (Middle and Upper Cambrian) at surface, covers 65 % of this area

Sandstone, siltstone, and shale; includes the Wonewoc Sandstone, Eau Claire Formation, and Mt. Simon Sandstone.

Upper Cambrian (Upper Cambrian) at surface, covers 26 % of this area

Sandstone, siltstone, shale, and dolostone; includes the Jordan Sandstone and St. Lawrence Formation, and the Mazomanie, Lone Rock, and Davis Formations of the Tunnel City Group.

Clam Falls volcanic sequence (Mesoproterozoic) at surface, covers 4 % of this area

Clam Falls volcanic sequence (~1,102 Ma).

Sandstone, siltstone, and local conglomerate (Mesoproterozoic) at surface, covers 3 % of this area

Sandstone, siltstone, and local conglomerate. Includes the Hinckley Sandstone and Fond du Lac (youngest detrital zircons ~1,000 Ma) and Solar Church Formations; deposition in eolian, fluvial, and lacustrine environments.

Chengwatana volcanic rocks (Mesoproterozoic) at surface, covers 2 % of this area

Primarily mafic flows.

Cambrian, undivided (Cambrian) at surface, covers 0.7 % of this area

Sandstone with some dolomite and shale, undivided; includes Trempealeau, Tunnel City, and Elk Mound Formations

Middle and Upper Ordovician (Middle and Upper Ordovician) at surface, covers 0.3 % of this area

Shale, dolomitic limestone, and sandstone; includes the Decorah Shale of the Galena Group, the Platteville and Glenwood Formations, and the St. Peter Sandstone.

Lower Ordovician (Lower Ordovician) at surface, covers < 0.1 % of this area

Dolostone, sandy to silty dolostone, and sandstone; includes the Shakopee Formation and Oneota Dolomite of the Prairie du Chien Group.

Prairie du Chien Group (Ordovician) at surface, covers < 0.1 % of this area

Dolomite with some sandstone and shale; includes Shakopee and Oneota Formations

Chengwatana Volcanic Group (Middle Proterozoic) at surface, covers < 0.1 % of this area

Gray basalt flows, interflow breccia, tuff, and minor sedimentary rocks