Geologic units in Bonner county, Idaho

Additional scientific data in this geographic area

Glacial deposits. (Pleistocene) at surface, covers 24 % of this area

Till and outwash consisting of gravel, sand, silt, and clay. Formed by valley glaciers at higher elevations and by the Cordilleran ice sheet in northern Idaho. Includes deposits of several glacial episodes. Includes rock glacier deposits and some modern alluvium derived from reworked till and outwash. (Quaternary Sediments).

Prichard Formation. (Mesoproterozoic) at surface, covers 21 % of this area

Siltite, quartzite, and argillite in northern Idaho; deposited in deep water and contains voluminous ~1470 Ma mafic sills. Includes siltite, quartzite, fine-grained schist, and carbonate rocks structurally above anorthosite near Boehls Butte, northeast of Elk River. (Mesoproterozoic Belt Supergroup).

Gneiss, schist, and quartzite. (Mesoproterozoic) at surface, covers 12 % of this area

Kyanite and sillimanite gneiss, schist, quartzite, and amphibolite that is metamorphosed lower part of Prichard Formation (Hauser Lake Gneiss) and underlying quartzite of Gold Cup Mountain in the Priest River metamorphic complex. (Mesoproterozoic Belt Supergroup).

Granodiorite and two-mica granite. (Cretaceous) at surface, covers 12 % of this area

Granodiorite and granite containing biotite, commonly with muscovite; includes bulk of Atlanta lobe (85-67 Ma) and isolated plutons in northern Idaho (107-67 Ma). (Paleocene and Cretaceous Idaho Batholith and Older Cretaceous and Jurassic Intrusive Rocks).

Missoula Flood deposits. (Pleistocene) at surface, covers 8 % of this area

Gravel, sand, and silt near Coeur d'Alene and Sandpoint that were carried by outburst floods from Glacial Lake Missoula (20-15 ka). Floods also flowed back up the Snake and Clearwater rivers to Kamiah. Missoula Flood slack-water deposits cover Lake Bonneville deposits in the Lewiston area. (Quaternary Sediments).

Tonalite, granodiorite, and quartz diorite. (Cretaceous) at surface, covers 6 % of this area

Tonalite, granodiorite, and quartz diorite, typically hornblende-bearing; includes the Payette River tonalite (~90 Ma) along western border zone of the Atlanta lobe, and the ~99 Ma Croesus pyroxene-biotite quartz diorite south of Hailey. Also includes granodiorite with potassium feldspar megacrysts that is typically hornblende-bearing and foliated (~90 Ma in central Idaho and ~100 Ma in northernmost Idaho) and early mafic phases of the Bitterroot lobe (~70 Ma). (Paleocene and Cretaceous Idaho Batholith and Older Cretaceous and Jurassic Intrusive Rocks).

Ravalli Group. (Mesoproterozoic) at surface, covers 3 % of this area

Feldspathic quartzite and subordinate siltite and argillite of the Burke, Revett, and St. Regis formations in northern Idaho; south of St. Joe River, includes correlative garnet-grade quartzite and schist. (Mesoproterozoic Belt Supergroup).

Challis intrusive rocks. (Eocene) at surface, covers 3 % of this area

Shallow roots of Challis volcanic field. Older suite of granodiorite and quartz monzodiorite and subordinate diorite, granite, and subvolcanic dacite; includes Jackson Peak, Beaver Creek, Marsh Creek, and Summit Creek stocks (49-45 Ma). Younger suite of granite and minor syenite and subvolcanic rhyolite; includes Sawtooth, Casto, Bungalow, and Lolo Hot Springs plutons (47-43 Ma). (Eocene Challis Magmatic Complex and Related Sedimentary Rocks).

Piegan Group. (Mesoproterozoic) at surface, covers 3 % of this area

Calcareous and dolomitic siltite, quartzite, and subordinate argillite of the Helena and Wallace formations in northern Idaho; south of St. Joe River, correlative rocks include garnet grade feldspathic quartzite and calc-silicate gneiss. (Mesoproterozoic Belt Supergroup).

Lower Missoula Group. (Mesoproterozoic) at surface, covers 2 % of this area

Siltite, argillite, and dolomitic siltite in northern Idaho; includes Snowslip and Shepard formations, rocks previously mapped as upper member of Wallace Formation, and correlative garnet-grade phyllite and schist south of St. Joe River. Also includes schist, micaceous quartzite, and calc-silicate rocks in lower part of Meadow Creek metamorphic sequence east of Elk City, and argillite, siltite, phyllite, and calc-silicate rocks south of Lost Trail Pass. (Mesoproterozoic Belt Supergroup).

Upper Missoula Group. (Mesoproterozoic) at surface, covers 2 % of this area

Feldspathic quartzite and subordinate siltite and argillite. Includes Mount Shields, Bonner, Striped Peak, and Libby formations in northern Idaho and possibly correlative quartzite north of Salmon and in the Meadow Creek metamorphic sequence east of Elk City. (Mesoproterozoic Belt Supergroup).

Alluvial deposits. (Quaternary) at surface, covers 1 % of this area

Deposits in valleys consisting of gravel, sand, and silt. Includes younger terrace deposits. May contain some glacial deposits and colluvium in uplands. (Quaternary Sediments).

Sedimentary rocks (Ordovician and Cambrian). (Ordovician and Cambrian) at surface, covers 1 % of this area

Marine limestone, dolomite, and subordinate shale and sandstone of Cambrian carbonate bank of southeast Idaho stratigraphically up to St. Charles Formation and Ordovician Garden City Limestone. Includes Bayhorse succession (Cash Creek Quartzite, Garden Creek Phyllite, Bayhorse Dolomite, Ramshorn Slate, and Clayton Mine Quartzite) of Clayton area and Pioneer Mountains; quartzite of Kamiak Butte north of Moscow; and Cambrian Gold Creek quartzite, Rennie Shale, and Lakeview Limestone east of Bayview. (Paleocene to Neoproterozoic Sedimentary and Igneous Rocks of the Cordilleran System).

Tonalitic orthogneiss and foliated granodiorite. (Cretaceous) at surface, covers 0.6 % of this area

Orthogneiss (primarily tonalite) and foliated granodiorite (~90 to ~80 Ma). Includes early phases of the Idaho batholith, migmatite, intrusions along major structures, and plutonic rocks of uncertain age along the Salmon River northwest of Salmon. (Paleocene and Cretaceous Idaho Batholith and Older Cretaceous and Jurassic Intrusive Rocks).

Metasedimentary rocks. (Paleozoic to Mesoproterozoic) at surface, covers 0.4 % of this area

Quartzite, feldspathic quartzite, calc-silicate gneiss, biotite gneiss, schist, and amphibolite north and east of McCall and as pendants in the southern part of the Idaho batholith; schist, quartzite, and marble in southwestern Idaho; argillite, siltite, quartzite, carbonate bearing quartzite, dolomite, phyllite, and conglomerate of the Deer Trail Group in northwest corner of state; and quartzite, Hayden Creek diamictite, and siltite stratigraphically above(?) the Swauger Formation south of Salmon. (Metasedimentary Rocks of Uncertain Age (Neoproterozoic to Paleoproterozoic)).

Mesozoic granitic rocks, undivided (Mostly Cretaceous-Jurassic) at surface, covers 0.2 % of this area

Granite, quartz monzonite, quartz diorite, granodiorite, and trondhjemite. Includes diorite in southeastern Washington; diorite and gabbro near Concunully in Okanogan County; gneiss, schist, and migmatites in areas of Chelan, Colville, and Okanogan batholiths. Includes high-grade metamorphic rocks of Precambrian age in Spokane area.

Laclede augen gneiss. (Mesoproterozoic) at surface, covers 0.1 % of this area

Biotite granite augen gneiss southeast of Priest River (~1575 Ma). Unit is in structural contact with surrounding rocks. Abundant alkali feldspar and high iron content indicate A-type granite composition. (Mesoproterozoic to Archean Basement Rocks).

Sedimentary rocks (Eocene). (Eocene) at surface, covers 0.1 % of this area

Fluvial, lacustrine, and air-fall deposits of conglomerate, volcanic sandstone, mudstone, and tuff near Challis, conglomerate north of Sandpoint, and conglomerate and sandstone of the Wasatch Formation in extreme southeastern Idaho. (Eocene Challis Magmatic Complex and Related Sedimentary Rocks).

Columbia River Basalt Group. (Miocene) at surface, covers 0.1 % of this area

Large-volume lava flows of tholeiitic basalt, basaltic andesite, and subordinate andesite in western Idaho; consists of Imnaha Basalt (17.5-16.5 Ma), Grande Ronde Basalt (16.5-15.6 Ma), Wanapum Basalt (15.6-14.5 Ma), and Saddle Mountains Basalt (14.5-6 Ma). Includes porphyritic basalt and basaltic andesite in western Owyhee County. (Quaternary to Eocene Continental Volcanic and Intrusive Rocks).

Precambrian rocks, undivided (Proterozoic) at surface, covers 0.1 % of this area

Predominantly phyllite with some schist, limestone, dolomite, quartzite, and volcanic rocks; northeastern Pend Oreille County. Mainly quartzite sandstone in upper part, dark-gray argillite with sandstone and limestone in middle part, and sandstone with argillite in lower part; southeastern Pend Oreille County. Banded slate with quartzite and dolomite; southwestern Stevens County. Quartzite, siliceous argillite, and argilliceous quartzite grading into argillite and quartz-mica schists form south ot north; southeastern Stevens County. Quartzite, argillite, quartz-feldspar gneiss, and other metamorphic rocks in northeastern Whitman and southeastern Spokane Counties are partly if not all extenstions of the Belt strata.

Glacial drift, undivided (Pleistocene) at surface, covers 0.1 % of this area

Glacial and glaciofluvial sand, gravel, and till; includes alpine glacier outwash and till as well as some Recent alluvium.

Metamorphic rocks. (Paleoproterozoic and Archean) at surface, covers < 0.1 % of this area

Pend Oreille granodiorite gneiss near Priest River (~2650 Ma); schist, gneiss, and subordinate quartzite along North Fork Clearwater River; Kelly Creek granite gneiss northeast of Pierce (~2670 Ma); orthogneiss in Pioneer Mountains (~2600 Ma and 695 Ma); granite gneiss, granite, schist, and amphibolite of Green Creek complex in Albion Mountains (~2600 Ma); granite gneiss in Beaverhead Mountains east of Leadore (~2450 Ma); and marble, quartzite, schist, and amphibolite of uncertain age near Henrys Lake. (Mesoproterozoic to Archean Basement Rocks).

Syenite and related rocks. (Cretaceous) at surface, covers < 0.1 % of this area

Syenite, monzonite, quartz monzonite, and subordinate pyroxenite (115-110 Ma); includes Gem stocks north of Wallace, Gold Hill stock northeast of Potlatch, Benning Mountain stock along the Montana-Idaho border east of Sandpoint, syenite of Wall Mountain north of Bonners Ferry, monzonite of Long Canyon (~88 Ma) northwest of Bonners Ferry, and no Business Mountain pluton (uncertain age) west of Donnelly. (Paleocene and Cretaceous Idaho Batholith and Older Cretaceous and Jurassic Intrusive Rocks).

Upper Missoula Group: McNamara, Bonner, and Mount Shields Formations; locally includes lower Libby Formation in northwestern Montana (Middle Proterozoic) at surface, covers < 0.1 % of this area

McNamara Formation: Dense green and red siltite and argillite in mudcracked couplets containing diagnostic chert beds and rip-up clasts. Thickness as much as 1,650 m (5,413 ft). Bonner Formation: Pink, cross-bedded, feldspathic, medium- to coarse grained quartzite. Thickness as much as 580 m (1,903 ft). Mount Shields Formation: Upper part: red quartzite, siltite, and argillite in mud-cracked couples and couplets with abundant salt casts. Lower part: light gray, flat-laminated, feldspathic, fine-grained quartzite. Thickness as much as 2,000 m (6,562 ft). In northwestern Montana - Libby Formation:Light to dark gray and greenish gray siltite and argillite with subordinate quartzite in mud-cracked couplets. Thickness as much as 2,300 m (7,546 ft).

Alluvium (Holocene) at surface, covers < 0.1 % of this area

Mostly unconsolidated silt, sand, and gravel valley fill with some clay; includes low-level terrace, marsh, peat, artificial fill, and glacial deposits locally.

Ravalli Group: St. Regis, Revett, and Burke Formations; or Empire and Grinnell Formations; or Empire and Spokane Formations (Middle Proterozoic) at surface, covers < 0.1 % of this area

St. Regis Formation: Green and purplish gray quartzite, siltite, and argillite in mud-cracked couples and couplets. Thickness as much as 900 m (2,953 ft). Revett Formation: Light gray, cross-bedded, felspathic, fine-grained quartzite. Thickness as much as 900 m (2,953 ft). Burke Formation: Gray or purple quartzite, siltite, and argillite in mud-cracked couples and couplets. Thickness as much as 1,000 m (3,281 ft). Empire Formation (Ye): Grayish green and pale olive gray argillite and siltite with subordinate thin beds of quartzite and sandy limestone. Thickness as much as 610 m. Grinnell Formation: White, cross-bedded sandstone or quartzite with red to purple siltite and argillite beds. Thickness as much as 1,160 m (3,806 ft). Spokane Formation (Ysp): Red siltite and argillite in mudcracked couplets. Thickness as much as 1,500 m (492 ft).

Gravel (Quaternary) at surface, covers < 0.1 % of this area

Variable deposits that range from pebble to boulder size and include sand, silt, and clay. Dominantly alluvial terrace, abandoned channel and floodplain, remnant alluvial fan, and local glacial outwash.

Upper Prichard or Appekunny Formation (Middle Proterozoic) at surface, covers < 0.1 % of this area

Upper Prichard Formation: Black and gray, pyritic siltite and argillite in planar couplets. Appekunny Formation: Gray and greenish gray argillite interbedded with light gray quartzite. Thickness as much as 1,700 m (5,577 ft).