Geologic units in Cook county, Minnesota

Basalt and basaltic andesite (Mesoproterozoic) at surface, covers 13 % of this area

Basalt and basaltic andesite. Includes the Leif Erickson, Lakeside (~1,098 Ma), Sucker River, Larsmont, Two Harbors, Crow Creek, Gooseberry River, Gustafson Hill, Baptism River, Good Harbor Bay, Cascade River, Croftville, Red Cliff, and Marr Island lavas.

Lower sequence, primarily basalt (Mesoproterozoic) at surface, covers 10 % of this area

Lower sequence, primarily basalt. Includes the Ely's Peak and Grand Portage basalts and Hovland lavas (~1,108 Ma).

Gabbroic intrusions (Mesoproterozoic) at surface, covers 10 % of this area

Gabbroic intrusions. Including the Sawmill, London, Brule River, Hovland, and Pigeon Point intrusions.

Rhyolite and icelandite (Mesoproterozoic) at surface, covers 8 % of this area

Rhyolite and icelandite. Includes the Cross River, Palisade Head (~1,096 Ma), Devil Track, Maple Hill, Grand Marais, and Kimball Creek lavas.

Granophyre, ferromonzodiorite, and leucogabbro (Mesoproterozoic) at surface, covers 7 % of this area

Granophyre, ferromonzodiorite, and leucogabbro. Includes the Mt. Weber (~1,106 Ma), Whitefish Lake (~1,109 Ma), Beth Lake, Misquah Hills (~1,106 Ma), and Cucumber Lake (~1,106 Ma) granophyres, and Wine Lake monzodiorite.

Gabbroic cumulates (Mesoproterozoic) at surface, covers 6 % of this area

Gabbroic cumulates. Includes the Poplar Lake (formerly Nathan's layered series) and Crocodile Lake intrusions (~1,107 Ma).

Slate and graywacke (Paleoproterozoic) at surface, covers 6 % of this area

Slate and graywacke. Includes the Rove (~1,836 to 1,777 Ma), Virginia (~1,832 Ma near base), and Thompson Formations (youngest zircons in the Thompson Formation ~1,790 Ma).

Anorthositic intrusions and inclusions, undifferentiated (Mesoproterozoic) at surface, covers 6 % of this area

Anorthositic intrusions and inclusions, undifferentiated (~1,099 Ma).

Saganaga Tonalite (Neoarchean) at surface, covers 5 % of this area

(~2,690 Ma) - Tonalite to granodiorite; typically contains large quartz phenocrysts and granodioritic to dioritic autoliths.

Felsic intrusive rocks, granophyre (Mesoproterozoic) at surface, covers 5 % of this area

Felsic intrusive rocks, granophyre. Includes parts of the Eagle Mountain (~1,098 Ma) and Pine Mountain (~1,095 to 1,098 Ma) intrusions.

Undifferentiated mafic to felsic lava flows (Mesoproterozoic) at surface, covers 5 % of this area

Undifferentiated mafic to felsic lava flows. Includes the Lakeside, Lakewood, and Cross River lavas.

Logan intrusions (Mesoproterozoic) at surface, covers 5 % of this area

Diabase and gabbro sills and dikes; locally porphyritic (~1,108, 1,115 Ma).

Diabase, gabbro, and ferromonzodiorite (Mesoproterozoic) at surface, covers 3 % of this area

Diabase, gabbro, and ferromonzodiorite. Primarily sills including the Endion, Lester River, Silver Cliff, Stony Point, Split Rock, Lafayette Bluff, Lake Clara–Lichen Lake, Pigeon River, and Reservation River intrusions.

Diabase and ferrodiorite (Mesoproterozoic) at surface, covers 2 % of this area

Diabase and ferrodiorite. Includes the Beaver River diabase, Silver Bay (~1,096 Ma), Milepost 7, Leveaux, Shoepack Lake, Cabin Creek, and Monker Lake intrusions.

Troctolite (Mesoproterozoic) at surface, covers 2 % of this area

Troctolite. Includes the Boulder Lake, Tuscarora (~1,099 Ma), Partridge River (~1,098 Ma), South Kawishiwi, and part of the Western Margin intrusions.

Schroeder-Lutsen basalts (Mesoproterozoic) at surface, covers 2 % of this area

Unconformably overlies units described below (Mns, Mnu, Mnr, and Mnb).

Troctolite, augite troctolite, and troctolitic gabbro of the Houghtaling Creek troctolite (Mesoproterozoic) at surface, covers 2 % of this area

Troctolite, augite troctolite, and troctolitic gabbro of the Houghtaling Creek troctolite (~1,099 Ma).

Undifferentiated volcanic rocks and volcanic hornfels (Mesoproterozoic) at surface, covers 0.8 % of this area

Undifferentiated volcanic rocks and volcanic hornfels.

Gabbro, ferrogabbro, and gabbronorite (Mesoproterozoic) at surface, covers 0.5 % of this area

Gabbro, ferrogabbro, and gabbronorite. Includes the Lax Lake and Cloquet Lake gabbros, Sonju Lake (~1,096 Ma), Dam Five, Wilson Lake (~1,096 Ma), Fourmile Lake, and Upper Manitou intrusions (~1,096 Ma).

Mafic to ultramafic (komatiitic) volcanic rocks (Neoarchean) at surface, covers 0.5 % of this area

Mafic to ultramafic (komatiitic) volcanic rocks. Includes the Newton Lake Formation and Deer Lake sequence.

Knife Lake Group volcanogenic lithic sandstone, conglomerate, siltstone, graywacke, and slate (Neoarchean) at surface, covers 0.3 % of this area

Volcanogenic lithic sandstone, conglomerate, siltstone, graywacke, and slate.

Interflow sandstone, siltstone, and conglomerate (Mesoproterozoic) at surface, covers 0.3 % of this area

Interflow sandstone, siltstone, and conglomerate.

Gunflint (~1,878 Ma), Biwabik, and Emily Iron Formations (Paleoproterozoic) at surface, covers 0.3 % of this area

Locally includes thin basal sandstone and conglomerate. Capped by an irregular layer of brecciated iron-formation and ejecta derived from the 1,850 Ma Sudbury meteorite impact.

Knife Lake Group conglomerate (Neoarchean) at surface, covers 0.2 % of this area

Knife Lake Group conglomerate. Clasts consist largely of hornblende-bearing volcanic rocks.

Knife Lake Group, hornblende-phyric volcanic flows, breccia, and tuff. (Neoarchean) at surface, covers 0.2 % of this area

Hornblende-phyric volcanic flows, breccia, and tuff.

Puckwunge and Nopeming Sandstones (Mesoproterozoic) at surface, covers < 0.1 % of this area

Puckwunge and Nopeming Sandstones.

Conglomerate, lithic sandstone, and graywacke, undifferentiated (Neoarchean) at surface, covers < 0.1 % of this area

Conglomerate, lithic sandstone, and graywacke, undifferentiated. Includes the Midway sequence, Seine Group, and a part of the Knife Lake Group known as the Ogishkemuncie conglomerate that contains clasts of ~2,690 Ma Saganaga Tonalite (unit Ast). Deposition of alluvial fan and fluvial sediments occurred in fault-bounded basins.

Syenite, monzodiorite, granodiorite, and diorite (Neoarchean) at surface, covers < 0.1 % of this area

Syenite, monzodiorite, granodiorite, and diorite. Commonly hornblende- or pyroxene-bearing; Includes the Coon Lake, Side Lake, and Linden (~2,666 Ma) plutons of north-central Minnesota.

Porphyritic quartzofeldspathic dikes (Neoarchean) at surface, covers < 0.1 % of this area

Porphyritic quartzofeldspathic dikes. Typically hypabyssal intrusions associated with felsic volcanic sequences.