Geologic units in Curry county, Oregon

Sedimentary rocks of Dothan Formation and related rocks (Late Jurassic to Early Cretaceous) at surface, covers 37 % 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 Jayko (unpublished data, 1985) in Curry and southern Coos Counties

Ultramafic and related rocks of ophiolite sequences (Paleozoic(?), Triassic(?), and Jurassic) at surface, covers 13 % 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 and A.S. Jayko (unpublished data, 1985).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

Colebrooke Schist (Paleozoic or Mesozoic) at surface, covers 10 % of this area

Metamorphosed pelitic sedimentary rocks and subordinate metamorphosed submarine pillow lavas and pyroclastic beds of basaltic composition. Metamorphic age is Early Cretaceous (about 130 Ma), according to Coleman (1972), and protolith may be Jurassic or older in age

Sedimentary rocks (Cretaceous) at surface, covers 7 % of this area

Marine graywacke, subgraywacke, conglomerate, and shale. Pebbles and cobbles in conglomerate are well rounded volcanic and metavolcanic rocks, low-grade metasedimentary rocks, quartzite, chert, and minor silicic and intermediate plutonic rocks. Shales are gray to black and are fissile to blocky. Sandstones commonly display graded bedding; conglomerate beds are commonly thick and poorly bedded. Shales, near Mitchell, have yielded latest (Early Cretaceous (Albian) fossils; some earliest Late Cretaceous (Cenomanian) fossils occur in beds southeast of Mitchell (D.L. Jones, oral Commun., 1972). Includes Hudspeth and Gable Creek Formations (OR049), Bernard Formation (OR028), and Cretaceous sedimentary rocks (OR008)

Sedimentary rocks of Dothan Formation and related rocks (Late Jurassic to Late Cretaceous) at surface, covers 7 % 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

Sedimentary rocks (Late Jurassic) at surface, covers 4 % 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)

Otter Point Formation of Dott (1971) and related rocks (Late Jurassic) at surface, covers 4 % of this area

Highly sheared graywacke, mudstone, siltstone, and shale with lenses and pods of sheared greenstone, limestone, chert, blueschist, and serpentine. Identified as melange by some investigators

Marine sandstone and siltstone (Middle Eocene) at surface, covers 3 % 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

Terrace, pediment, and lag gravels (Pleistocene to Holocene) at surface, covers 3 % 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)

Volcanic rocks (Late Jurassic) at surface, covers 2 % 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

Granite and diorite (Triassic and Jurassic) at surface, covers 2 % 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)

Myrtle Group (Late Jurassic to Early Cretaceous) at surface, covers 2 % of this area

Conglomerate, sandstone, siltstone, and limestone. Locally fossiliferous. As shown, includes Riddle and Days Creek Formations (Imlay and others, 1959; Jones, 1969)

Alluvial deposits (Holocene) at surface, covers 2 % 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

Marine siltstone, sandstone, and conglomerate (Early Eocene) at surface, covers 1 % of this area

Cobble and pebble conglomerate, pebbly sandstone, lithic sandstone, siltstone, and mudstone; massive to thin bedded; shelf and slope depositional setting. Contains foraminiferal faunas referred to the Penutian Stage of early Eocene age. Included by Diller (1898) in the Umpqua Formation; Baldwin (1974) and Ryberg (1984) included it in the Lookingglass Formation of the Umpqua Group of Baldwin; may be partly a shelf and slope facies of the sedimentary rocks of the Roseburg Formation of Baldwin (1974) according to Molenaar (1985) and Heller and Ryberg (1983)

Chetco complex of Hotz (1971) (Late Jurassic) at surface, covers 0.7 % 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

Marine sandstone, siltstone, and mudstone (Paleocene to Early Eocene) at surface, covers 0.5 % of this area

Rhythmically interbedded sandstone, siltstone, and mudstone with minor conglomerate; deposited in deep-sea fan depositional setting on submarine basalts of the Siletz River Volcanics. Contains foraminiferal faunas referred to the Penutian Stage of early Eocene age and locally contains assemblages of probable Paleocene age (McKeel and Lipps, 1975; P.D. Snavely, Jr. and David Bukry, written communication, 1980). Included by Diller (1898) in the Umpqua Formation; Baldwin (1974) and Ryberg (1984) mostly mapped unit as sedimentary rocks of the Roseburg Formation of the Umpqua Group; according to Heller and Ryberg (1983) and Molenaar (1985), may be partly correlative with the Lookingglass Formation of Baldwin (1974). Includes lower Eocene-Paleocene turbidite sedimentary rocks exposed at Five Mile Point, about 11 km north of Bandon, that are considered by Snavely and others (1980) to represent allochtonous terrane

Tyee Formation (Middle Eocene) at surface, covers 0.4 % of this area

Very thick sequence of rhymically bedded, medium- to fine-grained micaceous, feldspathic, lithic, or arkosic marine sandstone and micaceous carbonaceous siltstone; contains minor interbeds of dacite tuff in upper part. Foraminiferal fauna are referred to the Ulatisian Stage (Snavely and others, 1964). Groove and flute casts indicate deposition by north-flowing turbidity currents (Snavely and others, 1964), but probable provenance of unit is southwest Idaho (Heller and others, 1985)

Landslide and debris-flow deposits (Pleistocene to Holocene) at surface, covers 0.3 % 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

Volcanic rocks of the Dothan Formation and related rocks (Late Jurassic to Early Cretaceous) at surface, covers 0.3 % of this area

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

Lacustrine and fluvial sedimentary rocks (Pleistocene) at surface, covers 0.1 % of this area

Unconsolidated to semiconsolidated lacustrine clay, silt, sand, and gravel; in places includes mudflow and fluvial deposits and discontinuous layers of peat. Includes older alluvium and related deposits of Piper (1942), Willamette Silt (Allison, 1953; Wells and Peck, 1961), alluvial silt, sand, and gravel that form terrace deposits of Wells and others (1983), and Gresham and Estacada Formations of Trimble (1963). Includes deltaic gravel and sand and gravel bars, in pluvial lake basins in southeastern part of map area. In Rome Basin, includes discontinuous layers of poorly consolidated conglomerate characterized by well-rounded, commonly polished pebbles of chert and pebbles and cobbles of quartzite. In places contains mollusks or vertebrate fossils indicating Pleistocene age; mostly deposits of late Pleistocene age, but locally includes some deposits of early Holocene age. Includes Touchet Beds of Flint (1938), deposits of valley terraces of Newcomb (1965), and, in southeast Oregon, basin-filling deposits that incorporate Mazama ash deposits (Qma, Qmp) in the youngest layers

Amphibolite of Briggs Creek (Paleozoic or Mesozoic) at surface, covers 0.1 % 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)

Dune sand (Holocene) at surface, covers 0.1 % of this area

Large areas of windblown sand composed of rock-forming minerals, mostly feldspar and small amounts of quartz, and, in southeastern Oregon, also pumice

Alkalic intrusive rocks (Eocene to Oligocene) at surface, covers < 0.1 % of this area

Sills, dikes, stocks, and irregular intrusions of porphyritic or aphanitic camptonite, shonkinite, and. nepheline syenite or phonolite. Potassium-argon ages of 32 to 35 Ma obtained on camptonite and nepheline syenite (Snavely and others, 1976c; Fiebelkorn and others, 1983)

Saddle Mountains Basalt (Middle to Late Miocene) at surface, covers < 0.1 % of this area

Petrographically diverse flows of basalt erupted between about 13.5 and 6 Ma (McKee and others, 1977; Swanson and others, 1979)

Franciscan Complex, unit 1 (Coast Ranges) (Jurassic to Cretaceous) at surface, covers < 0.1 % of this area

Franciscan complex: Cretaceous and Jurassic sandstone with smaller amounts of shale, chert, limestone, and conglomerate. Includes Franciscan melange, except where separated--see KJfm.