Geologic units in Houghton county, Michigan

Additional scientific data in this geographic area

Jacobsville Sandstone (Middle Proterozoic) at surface, covers 62 % of this area

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

Oronto Group; Freda Sandstone (Middle Proterozoic) at surface, covers 16 % of this area

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

Portage Lake Volcanics (Middle Proterozoic) at surface, covers 11 % of this area

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

Baraga Group; Michigamme Formation, undivided (Early Proterozoic) at surface, covers 7 % of this area

Thick and stratigraphically varied formation of sedimentary and less abundant volcanic rocks. Metamorphosed graywacke is predominant rock of Michigamme Formation. Calcareous concretions common. Metamorphosed from cholorite to sillimanite grade (Cannon, 1986). Mapped undivided in poorly exposed areas

Copper Harbor Conglomerate (Middle Proterozoic) at surface, covers 3 % 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.

Oronto Group; Nonesuch Shale (Middle Proterozoic) at surface, covers 0.8 % of this area

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

Copper Harbor Conglomerate; Volcanic member (Early Proterozoic) at surface, covers 0.3 % of this area

Basaltic to andesitic volcanic flows interbedded within the conglomerate and sandstone

Powder Mill Group; Siemens Creek Volcanics (Middle Proterozoic) at surface, covers 0.3 % of this area

Dark-gray basalt and minor porphyritic andesite. Generally strongly magnetic with reversed remanent magnetism. Underlain by a thin unit of quartzose sandstone (Bessemer Quartzite).

Mellen Intrusive Complex; Granite (Middle Proterozoic) at surface, covers < 0.1 % of this area

Mellen Intrusive Complex; Granite (about 1000 Ma)

Paleozoic undivided (Paleozoic) at surface, covers < 0.1 % of this area

Paleozoic undivided