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Geologic units in Keweenaw county, Michigan

Additional scientific data in this geographic area

Portage Lake Volcanics (Middle Proterozoic) at surface, covers 63 % of this area

Lava flows, mostly basalt, andesite and felsite flows and subordinate interflow sedimentary rocks.

Jacobsville Sandstone (Middle Proterozoic) at surface, covers 21 % of this area

Red, brown, and white quartzose sandstone, and minor siltstone, shale and conglomerate

Copper Harbor Conglomerate (Middle Proterozoic) at surface, covers 14 % of this area

Red lithic conglomerate and sandstone; mafic to felsic volcanic flows similar to those of the unnamed formation (unit Yu) are interlayered with the sedimentary rocks.

Copper Harbor Conglomerate; Volcanic member (Early Proterozoic) at surface, covers 2 % of this area

Basaltic to andesitic volcanic flows interbedded within the conglomerate and sandstone

Oronto Group; Nonesuch Shale (Middle Proterozoic) at surface, covers 0.3 % of this area

Gray, green, and brown lithic siltstone, shale, and sandstone. Copper sulfides and native copper occur locally near base

Oronto Group; Freda Sandstone (Middle Proterozoic) at surface, covers 0.2 % of this area

Mainly reddish-brown, medium- to fine-grained lithic arkosic sandstone, siltstone, and micaceous silty shale.