Geologic units in Isanti county, Minnesota

Middle and Upper Cambrian (Middle and Upper Cambrian) at surface, covers 67 % 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 29 % 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.

Sandstone, siltstone, and local conglomerate (Mesoproterozoic) at surface, covers 2 % 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.

Mylonitic, gneissic, and schistose rocks of plutonic and volcanic protolith (Paleoproterozoic) at surface, covers 2 % of this area

Mylonitic, gneissic, and schistose rocks of plutonic and volcanic protolith.

Mafic intrusions including pyroxenite, peridotite, gabbro, and lamprophyre (Paleoproterozoic) at surface, covers < 0.1 % of this area

Mafic intrusions including pyroxenite, peridotite, gabbro, and lamprophyre. Defined largely by magnetic signature. One intrusion in Morrison County is ~1,791 Ma, and lithologically similar intrusions cut the Foley Granite (~1,774 Ma).