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Geologic units in Josephine county, Oregon

Ultramafic and related rocks of ophiolite sequences (Jurassic) (Paleozoic(?), Triassic(?), and Jurassic) at surface, covers 18 % of this area

Predominantly harzburgite and dunite with both cumulate and tectonite fabrics. Locally altered to serpentinite. Includes gabbroic rocks and sheeted diabasic dike complexes. Comprises Josephine ophiolite of Harper (1980), ophiolites of Onion Mountain, Sexton Mountain, Pearsoll Peak, Rogue River, and Riddle areas (Smith and others, 1982) and Coast Range ophiolite and serpentinite melange of M.C. Blake, Jr. and A.S. Jayko (unpublished data, 1985). In southwest Oregon, locally includes small bodies of early Mesozoic or late Paleozoic serpentinized and sheared ultramafic rocks, mostly in shear zones. Locally, volcanic and sedimentary rocks shown separately

Sedimentary rocks (Jurassic) (Late Jurassic ) at surface, covers 14 % of this area

Black and gray mudstone, shale, siltstone, graywacke, andesitic to dacitic water-laid tuff, porcelaneous tuff, and minor interlayers and lenses of limestone and fine-grained sediments metamorphosed to phyllite or slate. Locally includes some felsite, andesite and basalt flows, breccia, and agglomerate. Marine invertebrate fauna indicates age range from Early Jurassic (Hettangian) to early Late Jurassic (Oxfordian). In Klamath Mountains of southwest Oregon, includes Galice Formation (Wells and Peck, 1961) and unnamed, hornblende- and (or) pyroxene-bearing clastic rocks of Jurassic age (Smith and others, 1982)

Volcanic rocks (Triassic and Permian) (Triassic and (or) Jurassic) at surface, covers 12 % of this area

Massive flows of porphyritic meta-andesite, metabasalt, spilite, and keratophyre, volcanic breccia, and subordinate amounts of fine-grained volcaniclastic rocks. In southwest Oregon includes hornblende, pyroxene, and plagioclase porphyritic andesite flows, breccia, agglomerate, tuff, and locally, some basalt flows and dacitic tuffs of the Applegate Group

Lithology: andesite; basalt; dacite

Sedimentary rocks of Dothan Formation and related rocks (Lower Cretaceous and Upper Jurassic) (Late Jurassic to Early Cretaceous) at surface, covers 11 % of this area

Sandstone, conglomerate, graywacke, rhythmically banded chert lenses. Includes western Dothan and Otter Point Formations of M.C. Blake, Jr. and AS. Jayko (unpublished data, 1985) in Curry and southern Coos Counties

Shale, mudstone, and sandstone (Jurassic) (Late Jurassic) at surface, covers 7 % of this area

Black to gray shale, mudstone, and sandstone with local lenses of pebble conglomerate. Overlies Josephine ophiolite of Harper (1980) (unit Ju)

Granitic rocks (Cretaceous and Jurassic) (Late Jurassic and Early Cretaceous) at surface, covers 7 % of this area

Mostly tonalite and quartz diorite but including lesser amounts of other granitoid rocks. Potassium-argon ages determined on hornblende indicates plutons range in age from 143 to 166 Ma (Hotz, 1971)

Sedimentary rocks, partly metamorphosed (Triassic and Paleozoic) (Paleozoic to Jurassic(?)) at surface, covers 5 % of this area

Poorly bedded argillite, chert, phyllite, phyllitic quartzite, calc-phyllite, impure limestone, and marble. In places rocks are strongly foliated. In Klamath Mountains of southwest Oregon, includes shale, mudstone, volcaniclastic sandstone, graywacke, conglomerate, tuff, and minor radiolarian chert and marble of the Applegate Group

Volcanic rocks (Jurassic) (Late Jurassic) at surface, covers 4 % of this area

Lava flows, flow breccia, and agglomerate dominantly of plagioclase, pyroxene, and hornblende porphyritic and aphyric andesite. Includes flow rocks that range in composition from basalt to rhyolite as well as some interlayered tuff and tuffaceous sedimentary rocks. Commonly metamorphosed to greenschist facies; locally foliated, schistose or gneissic. Includes the Rogue Formation and volcanic rocks commonly assigned to the Galice Formation (Wells and Walker, 1953; Wells and Peck, 1961). Considered to be accreted island-arc terrane

Alluvial deposits (Holocene) (Holocene) at surface, covers 4 % of this area

Sand, gravel, and silt forming flood plains and filling channels of present streams. In places includes talus and slope wash. Locally includes soils containing abundant organic material, and thin peat beds

Lithology: sand; gravel; silt; peat

Terrace, pediment, and lag gravels (Holocene and Pleistocene) (Pleistocene to Holocene) at surface, covers 4 % of this area

Unconsolidated deposits of gravel, cobbles, and boulders intermixed and locally interlayered with clay, silt, and sand. Mostly on terraces and pediments above present flood plains. Includes older alluvium of Smith and others (1982) in the Klamath Mountains and both high- and low-level terraces along Oregon coast. Includes dissected alluvial fan deposits northeast of Lebanon, and Linn and Leffler Gravels of Allison and Felts (1956)

Melange (Jurassic) (Jurassic) at surface, covers 3 % of this area

Structurally complex mixture of basaltic rocks, serpentinite, chert, argillite, conglomerate, silty sandstone, and lenses of marble composing the melange of the Takilma area of Smith and others (1982)

Granite and diorite (Jurassic and Triassic) (Triassic and Jurassic) at surface, covers 3 % of this area

Felsic to intermediate, granitoid intrusive rocks. Includes Jurassic muscovite granodiorite, hornblende gabbro, tonalite, and quartz diorite of southwest Oregon (Smith and others, 1982)

Ultramafic and related rocks of ophiolite sequences; Basaltic volcanic and sedimentary rocks (Jurassic) (Jurassic) at surface, covers 3 % of this area

Basalt flows, flow breccia, agglomerate, pillow basalt and pillow breccia, and lesser shale, chert, siltstone, and mudstone of ophiolitic complexes

Lithology: basalt; mudstone; chert

Amphibolite of Briggs Creek (Mesozoic or Paleozoic) (Paleozoic or Mesozoic) at surface, covers 2 % of this area

Informally called the "Briggs Creek amphibolite" by Garcia (1976) and by Coleman and others (1976). Consists of amphibolite, micaceous quartzite, quartz schist, and recrystallized manganiferous chert. Includes structurally complex amphibole schist and quartz-rich hornblende gneiss of unknown age exposed at and near Chetco Peak west of Cave Junction (Smith and others, 1982)

Fanglomerate (Holocene? and Pleistocene) (Pleistocene to Holocene) at surface, covers 2 % of this area

Poorly sorted and poorly stratified alluvial fan debris, slope wash, colluvium, and talus; composed mostly of silt and fragments of basalt, basaltic andesite, and andesite. In places includes small areas of pediment gravels and colluvium

Gabbro and ultramafic rocks associated with granitic plutons (Cretaceous and Jurassic) (Late Jurassic and Early Cretaceous) at surface, covers 0.4 % of this area

Predominantly hornblende gabbro, gabbro, and olivine gabbro, but includes pyroxenite, hornblende pyroxene, and minor peridotite, dunite, and serpentinite (Smith and others, 1982)

Clastic sedimentary rocks (Upper and Lower Cretaceous) (Early to Late Cretaceous) at surface, covers 0.3 % of this area

Locally fossiliferous sandstone and conglomerate; marine fossils indicate Early Cretaceous (Albian) age (Jones, 1960). Includes the Hornbrook Formation of Peck and others (1956), the Grove Creek strata of Jones (1960) and Page and others (1977), Hunters Cove Formation, Cape Sebastian Sandstone, Humbug Mountain Conglomerate, and Rocky Point Formation (Dott, 1971; Blake and others, 1985) and clastic sedimentary rocks on the West Fork of the Illinois River near Waldo (Imlay and others, 1959), about 12 km south of Cave Junction

Volcanic rocks of the Dothan Formation and related rocks (Lower Cretaceous and Upper Jurassic) (Late Jurassic to Early Cretaceous) at surface, covers 0.2 % of this area

Basaltic pillow lavas, volcanic breccia, and silicified basalt lava flows

Lithology: basalt

Landslide and debris-flow deposits (Holocene and Pleistocene) (Pleistocene to Holocene) at surface, covers 0.2 % of this area

Unstratified mixtures of fragments of adjacent bedrock. Locally includes slope wash and colluvium. Largest slides and debris flows occur where thick sections of basalt and andesite flows overlie clayey tuffaceous rocks. May include some deposits of late Pliocene age

Lithology: landslide

Chetco complex of Hotz (1971) (Jurassic) (Late Jurassic) at surface, covers 0.2 % of this area

Informally named unit representing island-arc volcanic complex comprised predominantly of igneous and metamorphosed volcanic rocks; includes gabbro, metagabbro, quartz diorite, and amphibolite

Lithology: amphibolite

May Creek Schist (Paleozoic) (Paleozoic(?) to Jurassic) at surface, covers < 0.1 % of this area

Layered amphibolite, schist, gneiss, and quartzite. Protolith considered to be of Paleozoic age

Marine sandstone and siltstone (middle Eocene) (Middle Eocene) at surface, covers < 0.1 % of this area

Thin- to thick-bedded, crossbedded, well-sorted, fine- to medium-grain sandstone, siltstone, and mudstone; characterized by sparse fine white mica; shallow marine depositional setting at least partly of deltaic origin. Contains foraminiferal and molluscan faunas of early middle Eocene age. Included by Diller (1898) in the upper part of the Umpqua Formation, by Baldwin (1974) and Ryberg (1984) in the Flournoy Formation of the Umpqua Group, and by Molenaar (1985) in Camas Valley and the White Tail Ridge Members of Baldwin (1974) of the Umpqua Formation

Jurassic marine rocks, unit 1 (Western Sierra Nevada and Western Klamath Mountains) (Triassic to Late Jurassic) at surface, covers < 0.1 % of this area

Shale, sandstone, minor conglomerate, chert, slate, limestone; minor pyroclastic rocks

Mesozoic granitic rocks, unit 5 (Klamath Mountains) (Jurassic to early Cretaceous) at surface, covers < 0.1 % of this area

Mesozoic granite, quartz monzonite, granodiorite, and quartz diorite

Undivided pre-Cenozoic metavolcanic rocks, unit 2 (undivided) (Paleozoic(?) to Mesozoic(?)) at surface, covers < 0.1 % of this area

Undivided pre-Cenozoic metavolcanic rocks. Includes latite, dacite, tuff, and greenstone; commonly schistose.

Ultramafic rocks, chiefly Mesozoic, unit 2 (Western Sierra Nevada and Klamath Mountains) (Late Proterozoic(?) to Early Jurassic) at surface, covers < 0.1 % of this area

Ultramafic rocks, mostly serpentine. Minor peridotite, gabbro, and diabase. Chiefly Mesozoic unit 2

Mesozoic volcanic rocks, unit 2 (Western Sierra Foothills and Western Klamath Mountains) (Jurassic) at surface, covers < 0.1 % of this area

Undivided Mesozoic volcanic and metavolcanic rocks. Andesite and rhyolite flow rocks, greenstone, volcanic breccia and other pyroclastic rocks; in part strongly metamorphosed. Includes volcanic rocks of Franciscan Complex: basaltic pillow lava, diabase, greenstone, and minor pyroclastic rocks