U.S. DEPARTMENT OF THE INTERIOR TO ACCOMPANY MAP I–2542 

U.S. GEOLOGICAL SURVEY 

GEOLOGIC MAP OF THE RED BLUFF 30' × 60' QUADRANGLE, CALIFORNIA
 

By M.C. Blake, Jr., D.S. Harwood, E.J. Helley, W.P. Irwin, A.S. Jayko, and D.L. Jones
 

DESCRIPTION OF MAP UNITS 

SACRAMENTO VALLEY– 

CASCADE RANGE PROVINCE 

Sedimentary rocks 

t Dredge tailings (Holocene)—Also includes other 

ground disturbed by man 

Qsc Stream channel deposits (Holocene)—Gravel, 

sand, and silt deposited in open, active stream 

channels without permanent vegetation. 

Deposits are being transported under modern hydrologic conditions, and, consequently, 

are light colored (tan and gray), unweathered, and usually in contact with modern 

surface waters. Thickness varies from 25 m 

on Sacramento River to less than a few centimeters in bedrock canyons 

Qa Alluvium (Holocene)—Gravel, sand, and silt 

deposited by present-day streams and rivers; 

derived from Tehama and Tuscan Formations and from rocks in Coast Ranges and 

Klamath Mountains. Differentiated from 

older and younger units chiefly on the basis 

of geomorphic position in modern stream 

channels 

Qo Overbank deposits (Holocene)—Sand, silt, and 

minor lenses of gravel deposited by floods 

and high-water stages on low terraces adjacent to present-day alluvial channels 

Qao Alluvial and overbank deposits, undivided 

(Holocene)—Gravel, sand, and silt deposited by normal and high-water flows in 

modern streams 

Qb Basin deposits (Holocene)—Fine-grained silt 

and clay 

Modesto Formation (Pleistocene)—Deposits 

in two terraces that show very fresh dispositional morphology and little, if any, erosional features. Terraces probably were 

deposited by same stream systems that flow 

today because they generally border existing channels. Derived from heterogeneous 

metamorphic, sedimentary, and volcanic 

rocks. Divided into: 

Qmu Upper member—Gravel, sand, silt, and clay 

found on lower Modesto terrace. Lithologically similar to lower member except that 

soils lack pedogenic B horizon. Unit is less 

than 3 meters thick 

Qml Lower member—Gravel, sand, silt, and clay 

found on upper Modesto terrace. Soils contain 

pedogenic B horizon. Unit is less than 5 

meters thick 

Riverbank Formation (Pleistocene)—Deposits 

in two terraces cut and filled into surface 

of Red Bluff Formation. Divided into: 

Qru Upper member—Gravel, sand, silt, and clay 

found on lower Riverbank terrace. Lithologically similar to Modesto Formation but differentiated from it on the basis of both higher 

geomorphic position and greater degree of 

soil formation. Soils display medial development with strong textures, B horizons, and 

local hardpans. Lithologically very similar 

to, but more widespread than, lower member. Terrace surfaces are geomorphically 

lower and generally smoother than those of 

lower member, and, in addition, soil profile is not as well developed as that on lower 

member. Unit is less than 10 meters thick 

Qrl Lower member—Gravel, sand, silt, and clay 

found on higher Riverbank terrace. Derived 

from heterogeneous metamorphic, sedimentary, and volcanic rocks; lithologically similar to Red Bluff Formation but is slightly 

finer grained and contains less gravel. 

Lower member is more eroded than upper member 

Qrb Red Bluff Formation (Pleistocene)—Very coarse, 

red (2.5–5YR) gravel that contains minor 

amounts of interstratified sand and silt. Red 

Bluff deposits located west of Sacramento 

River were derived from metamorphic rocks 

of Coast Ranges and Klamath Mountains. 

Volcanic-clast fanglomerate in eastern part 

of quadrangle was derived from Tuscan 

Formation and lava flows and is correlated 

with Red Bluff Formation to west. All 

Quaternary alluvial deposits except older 

gravel deposits (unit QTog) are deposited 

1
 
in channels eroded into Red Bluff Formation. Red Bluff Formation is overlain by 0.4– 

Ma Rockland ash bed of Sarna-Wojcicki and 

others (1982), and it overlies olivine basalt 

of Deer Creek (1.08 Ma; Harwood and others, 

1981) 25 km southeast of city of Red Bluff. 

Maximum thickness is 5 m 

QTog Older gravel deposits (Pleistocene and (or) 

Pliocene)—Reddish- to yellowish-tan, 

moderately well indurated coarse gravel and 

minor amounts of coarse sand that rest 

unconformably on eroded soil profile developed on Tuscan Formation near The Hogback and in Salt Creek east of city of Red 

Bluff. Clasts are well-rounded, locally deeply 

weathered volcanic fragments apparently 

derived from Tuscan Formation. At Deer 

Creek, 5 km south of quadrangle, older gravel 

deposits unconformably underlie olivine basalt of Deer Creek (1.08 Ma; Harwood and Qip 

others, 1981). Red Bluff Formation 

unconformably overlies older gravel deposits 

in Salt Creek. Maximum thickness is 65 m 

Tte Tehama Formation (Pliocene)—Fluvial deposits 

of pale-green, gray, and tan sandstone, 

tuffaceous sandstone, and siltstone and lenses 

of crossbedded pebble and cobble conglomerate derived both from metamorphic rocks 

of Coast Ranges and Klamath Mountains and 

from volcanic rocks of Tuscan Formation. 

Interfingers with Tuscan Formation in vicinity of Sacramento River. Maximum thickness is about 600 m near city of Red Bluff. 

Locally includes: 

Tten Nomlaki Tuff Member—Dacitic pumice tuff 

found at or near base of both Tehama and Qiu 

Tuscan Formations; see description under 

Tuscan Formation in subsection entitled 

“Volcanic rocks” 

Tc Channel deposits (Pliocene and (or) Miocene)— 

Tan or yellowish-tan to reddish-brown cobble 

conglomerate and sandstone exposed below 

Nomlaki Tuff Member of Tuscan Formation 

at Tuscan Springs and in some deeper 

canyons along Chico Monocline southeast Qbc 

of quadrangle. Well-rounded clasts include 

greenstone, gray quartzite, red, green, and 

black chert, white vein quartz, and lesser 

amounts of green and gray phyllite. Varied 

amounts of subrounded basalt and basalticandesite clasts are intermixed with metamor- Qbb 

phic rock fragments. Maximum thickness is 

about 20 m 

Kc Chico Formation (Late Cretaceous)—Tan, 

yellowish-brown to light-gray, fossiliferous 

marine sandstone; lenticular beds of pebble 

to cobble conglomerate; and minor siltstone. 

Exposed at Tuscan Springs, in Salt Creek, 

and in Sevenmile Creek south of Tuscan 

Buttes. Conglomerate clasts are rounded to 

well rounded and consist of red, green, and 

black chert, white vein quartz, quartzite, 

granite, and greenstone. Calcite cement and 

fossil fragments are common at Tuscan 

Springs. Sandstone is composed of fine- to 

medium-grained, angular to subrounded 

grains of quartz, plagioclase, alkali feldspar, 

lithic fragments, and detrital chert. Thickness is unknown 

Volcanic rocks 

Basaltic rocks of Inskip Hill volcanic center 

(Holocene)—Divided into: 

Basalt flow of Paynes Creek—Thin, black to 

dark-gray, olivine-bearing, high-alumina, 

diktytaxitic basalt flow. Erupted from Inskip 

Hill, 5 km east of Soap Butte; flowed 

westward in Inks Creek and Paynes Creek, 

reaching Sacramento River at Chinese 

Rapids. Northeast of Dales near quadrangle 

boundary, thickness of Paynes Creek basalt 

flow is about 8 m; at Manton Road 2 km 

northeast of Dales Lake, about 2 m; at 

Chinese Rapids, about 10 m. Age of Paynes 

Creek basalt flow is unknown but must be 

about 10,000 yr B.P. or less because flow 

overlies alluvium assigned to upper member of Modesto Formation in tributary of Inks 

Creek 

Basalt flows of Inskip Hill and Soap Butte, 

undivided—Several high-alumina olivine 

basalt flows that originate at Soap Butte and 

Inskip Hill, 5 km east of Soap Butte. Thickness of flows is unknown but their limited 

distribution suggests that they are thin, nearvent deposits 

Basaltic rocks of Black Butte volcanic center 

(Holocene)—Divided into: 

Cinder deposits—Black, well-bedded, fine- to 

coarse-grained basaltic cinders, which form 

dissected ejecta blanket that ranges in thickness from about 10 m in cinder pit on Ash 

Creek to about 1.5 m on south rim of Lack 

Creek near northeast corner of quadrangle 

Basalt flow of Black Butte—Black to lightgray, high-alumina olivine basalt flow, 

which issued from vent that ultimately built 

Black Butte cinder cone 0.5 km east of 

quadrangle. One branch of flow moved 

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about 1 km west of vent into upper reaches 

of Rancheria Creek; other branch cascaded 

over Battle Creek Fault scarp just east of 

quadrangle boundary. Basalt consists of 

olivine and clinopyroxene phenocrysts 

scattered in diktytaxitic matrix of 

clinopyroxene and plagioclase; accessory 

minerals include abundant magnetite in 

matrix and minor amounts of euhedral 

spinel within olivine phenocrysts. Maximum thickness is 6 m 

Qtbb Basalt near Tuscan Buttes (Holocene and (or) 

Pleistocene)—Gray, reddish-gray to black, 

glomeroporphyritic to highly vesicular, 

high-alumina basalt and minor amounts of 

scoria. Exposed on west flank of Tuscan 

Buttes and in Sevenmile Creek to southwest. Morphology of deposits suggests 

small, local extrusions of basalt along 

approximately north trending fissure system 

after much, if not all, of present local relief 

on surface of Tuscan Formation had formed 

by uplift and erosion 

Qab Hypersthene andesite of Brokeoff Mountain 

(Pleistocene)—Porphyritic hypersthene 

andesite channeled along Battle Creek Fault 

Zone in northeast part of quadrangle. Unit 

is continuous with andesite of Brokeoff 

Mountain mapped by Macdonald and 

Lydon (1972) in Whitmore 15' quadrangle. 

Rock is dark gray to black and contains 

abundant white plagioclase phenocrysts as 

long as 5 mm. Scattered glomeroporphyritic 

aggregates of plagioclase, honey-yellow 

phenocrysts of hypersthene, and rare augite 

are set in fine-grained matrix of plagioclase microlites and brown glass. Flow is 

about 6 m thick 

Qr Rockland ash bed of Sarna-Wojcicki and others (1982) (Pleistocene)—Loosely aggregated, dacitic pumice lapilli ash (Wilson, 

1961) that contains scattered, coarse, white 

pumice fragments as much as 20 cm in 

diameter. Pumiceous fragments are composed primarily of silky white, wispy, 

vesicular glass that contains scattered 

crystals of glassy to white plagioclase and 

sanidine, green hornblende, hypersthene, 

and minor magnetite. Found as scattered 

erosional remnants of large, nonwelded ashflow sheet that erupted 34 km east of 

quadrangle. North of Digger Buttes, about 

15 km east of quadrangle, ash-flow tuff 

is at least 60 m thick but is generally less 

than 5 m thick in scattered patches to west. 

Fission-track age of 0.4 Ma (C.E. Meyer 

and A.M. Sarna-Wojicki, unpub. data, 1984, 

in Sarna-Wojicki and others, 1985; see also, 

Meyer and others, 1991) 

Basalt flows of Shingletown Ridge (Pleistocene)—At least three flows of highalumina olivine basalt exposed in 

northeastern part of quadrangle. Flows were 

mapped in Whitmore 15' quadrangle by 

Macdonald and Lydon (1972) and traced 

eastward to Red Mountain Lake area in 

Manzanita Lake 15' quadrangle by 

Macdonald (1963), where they apparently 

originated from several vents along fissure system that trends north-northwest 

from vicinity of Lassen Peak. Dark-gray, 

fine-grained, diktytaxitic and locally porphyritic basalt contains rounded phenocrysts of brownish-green olivine scattered 

in openwork-mesh matrix of plagioclase 

and clinopyroxene. Maximum thickness of 

individual flows is about 5 m. Divided into: 

Qsf3 Flow 3 

Qsf2 Flow 2 

Qsf1 Flow 1 

Qeb Olivine basalt of Eagle Canyon (Pleistocene)— 

Dark-gray, diktytaxitic, vesicular olivine 

basalt exposed on walls of Eagle Canyon 

(1 km east of quadrangle) in Battle Creek 

along foot of Battle Creek Fault scarp above 

coarse bouldery volcanic fanglomerate. 

Wilson (1961, p. 11) grouped rocks comprising olivine basalt of Eagle Canyon, 

fanglomerate mapped as Red Bluff Formation in this report, and underlying basalt 

of Coleman Forebay into his Long Ranch 

basalt unit. Maximum thickness is about 

4 m; source unknown 

Qbd Olivine basalt of Devils Half Acre (Pleistocene)—Gray, glomeroporphyritic, vesicular olivine basalt that shows well-developed 

columnar jointing on north rim of Antelope Creek. Aggregates of strongly zoned 

plagioclase as much as 10 mm in diameter and euhedral to subhedral olivine as 

much as 5 mm in diameter are set in ophitic 

matrix of nearly equal amounts of plagioclase microlites and clinopyroxene. Magnetite is scattered in matrix; knee-shaped 

twinned high-relief crystals of rutile(?) 

included in plagioclase microlites. Maximum thickness is 15 m; source unknown 

Qcb Basalt of Coleman Forebay (Pleistocene)— 

Olivine basalt flows that underlie volcanic fanglomerate, correlated with the Red 

3
 
Bluff Formation, in several isolated areas 

that extend from Coleman Forebay on 

Battle Creek Fault scarp southward to 

vicinity of Hog Lake. Rock is light-rustygray-weathering, dark-gray olivine basalt 

that has pronounced diktytaxitic texture, 

as well as scattered large vesicles and voids 

that form large rounded pits on weathered 

surfaces. Maximum thickness is 10 m; 

source unknown 

QTa Andesite (Pleistocene and (or) Pliocene)—Gray, 

greenish-gray, red, and grayish-tan, finegrained, sparsely porphyritic, locally flowbanded andesite preserved as erosional 

remnant of larger flow that caps Tuscan 

Buttes. Phenocrysts of basaltic hornblende 

variably altered to dustlike particles of 

magnetite are set in matrix of oriented, flowtrained microlites of plagioclase. Interstices 

are filled with either very fine grained Tti 

plagioclase(?) or silica mineral after glass. 

Maximum thickness is 35 m; source unknown 

Tuscan Formation (Pliocene)—Divided into: 

Ttu Undivided part—Interbedded lahar deposits, 

volcanic conglomerate, volcanic sandstone, 

and pumiceous tuff 

Ttd Member D—Block-and-ash deposits composed of juvenile andesitic pyroclastic 

debris and interbedded lahar deposits; 

characterized by large monolithologic 

masses of gray hornblende andesite, augiteolivine basaltic andesite, and black pumiceous mudstone, as well as smaller 

fragments of black obsidian and white and 

gray, hornblende-bearing pumice, all in 

grayish-tan pumiceous-mudstone matrix. 

Distinguished from member C by presence Ttb 

of large, fractured monolithologic rock 

masses, black obsidian fragments, and white 

and dove-gray pumice fragments. Thickness ranges from about 10 to 50 meters 

Tth Tuff member of Hogback Road—Discontinuous unit of well-bedded lapilli tuff, pumiceous conglomerate, and sandstone. Contains 

abundant, well-rounded, white, hornblendebearing dacitic pumice clasts as much as 3 

cm in diameter and lesser amounts of smaller, 

well-rounded, light-gray and black andesitic pumice clasts. Tuff rests unconformably 

on deformed and locally eroded older units Tta 

of Tuscan Formation but appears to be 

conformable beneath member D. At The 

Hogback, thickness of tuff is 1 m; on north 

side of Tuscan Buttes, about 4 m 

Ttc Member C—Predominantly lahar deposits composed of angular to subrounded volcanic fragments as much as 3 m in diameter in matrix 

of grayish-tan volcanic mudstone. Both composition and texture of fragments, as well 

as ratio of fragments to matrix, are highly 

varied. Scattered large irregular masses of 

brick-red and gray, commonly massive to 

locally flow-banded volcanic breccia are 

present within lahar deposits throughout 

quadrangle. Poorly sorted, polymict volcanic 

conglomerate, sandstone, and siltstone are 

interlayered with lahar deposits and increase 

in abundance toward west and south. Lahar deposits are generally reversely graded 

and range in thickness from about 0.5 m to 

10 m; upper and lower contacts are sharp. 

Total thickness of member C is at least 75 

m where exposed in western part of Antelope Creek 

Ishi Tuff Member—Indurated but nonwelded, 

white to light-gray, fine-grained pumiceous 

air-fall tuff commonly reworked and contaminated with varied amounts of volcanic sandstone and siltstone. Readily 

distinguished by abundant bronze-colored 

mica flakes about 1 mm in diameter. Along 

Chico Monocline, Ishi Tuff Member locally separates members B and C. Preliminary potassium-argon ages obtained on 

biotite, hornblende, and plagioclase separated from pumice clasts are widely discordant; zircons from pumice clasts give 

fission-track age of about 2.6 Ma, which is 

currently best estimate of age of Ishi Tuff 

Member. Maximum thickness is 30 cm; 

source unknown 

Member B—Interbedded lahar deposits and 

volcanic conglomerate, and volcanic sandstone and siltstone; lithologically similar to 

rocks of member C except that volcanic 

conglomerate and volcanic sandstone are 

more abundant in member B. Lahar deposits 

and alluvial volcaniclastic rocks are 

interbedded in approximately equal proportions, giving more regularly layered sequence 

than in lahar-rich member C. Maximum 

thickness of conglomerate layers is about 

15 m; total thickness of member B is about 

130 m along Chico Monocline 

Member A—Interbedded lahar deposits, volcanic conglomerate, volcanic sandstone, 

and siltstone, all containing scattered fragments of metamorphic rocks. Metamorphicrock fragments, which include white vein 

quartz, green, gray, and black chert, green4
 
 

stone, greenish-gray slate, and serpentinite, 

make up less than 1 percent of rock type. 

Top of member A is defined by highest 

lahar deposit or volcanic-conglomerate 

layer that contains metamorphic-rock fragments. Exposures of member A in quadrangle are found only in canyon of Dye 

Creek. Thickness is unknown 

Ttn Nomlaki Tuff Member—White, light-gray, 

locally reddish-tan to pink, dacitic pumice tuff and pumice lapilli tuff at or very 

near base of both Tuscan and Tehama Formations. Pumice fragments as much as 20 

cm in diameter are generally white in lower 

part of member and mixture of white and 

light- and dark-gray in upper part. Member is generally massive, nonwelded, 

nonlayered ash-flow tuff well exposed at 

Tuscan Springs, on Antelope Creek, and 

at Gas Point on Cottonwood Creek, as well 

as at several localities south of Gas Point 

along west margin of valley. Maximum 

thickness is 25 m at Tuscan Springs, about 

20 m at Antelope Creek, and 10 m at Gas 

Point. Age of Nomlaki given by Evernden 

and others (1964) as 3.4 Ma 

Taa Basaltic andesite of Antelope Creek (Pliocene)— 

Dark-gray to greenish-gray, locally altered 

to brick-red and reddish-gray, massive, highly 

fractured, fine-grained, sparsely vesicular 

basaltic andesite exposed in Antelope Creek 

and, to lesser extent, in Salt Creek. Red and 

reddish-gray scoria layers about 1 m thick 

alternate with layers of massive gray basaltic andesite of about equal thickness in 

western exposures of Antelope Creek and 

Salt Creek, suggesting that these exposures 

are near distal end of flow. Whole-rock 

potassium-argon age of 3.99±0.12 Ma. Maximum thickness is 15 m 

SACRAMENTO VALLEY–WESTERN 

FOOTHILLS PROVINCE 

Overlap assemblage (Late and Early Cretaceous)—Marine sedimentary rocks of Great 

Valley sequence. Unconformably overlies 

basement rocks of Klamath Mountains and 

disconformably overlies sedimentary rocks 

of Elder Creek terrane. Age of unit is 

Hauterivian to Coniacian. Divided into: 

Koms Mudstone—Dark-gray mudstone and minor 

thin interbeds of siltstone and fine-grained 

sandstone; where mapped, interlayered with 

sandstone and conglomerate of unit Koss 

Koss Sandstone and conglomerate—Fine- to 

coarse-grained sandstone and local pebble 

to boulder conglomerate; derived from older 

Klamath Mountains terranes, as well as 

volcanic and plutonic sources, including 

Shasta Bally batholith 

Elder Creek terrane—Divided into: 

ecms Mudstone (Early Cretaceous and Late Jurassic)—Dark-gray, hackly-fractured mudstone that contains minor tan siltstone and 

sandstone; nodules, lenses, and thin beds of 

limestone locally abundant. Relatively 

nonresistant unit forms valleys and swales 

parallel to strike 

ecss Sandstone and conglomerate (Early Cretaceous and Late Jurassic)—Fine- to coarsegrained sandstone, local conglomerate, and 

minor interbedded mudstone. Relatively 

resistant unit forms prominent topographic 

ridges parallel to strike 

Coast Range ophiolite (Late and Middle 

Jurassic)—Dismembered ophiolite. Divided into: 

ecg	 Layered gabbro—Alternating discontinuous layers of plagioclase- and pyroxenerich gabbro. Includes minor intercalations 

of layered ultramafic rocks (wehrlite, 

clinopyroxenite, and dunite) 

ecu	 Layered ultramafic rocks—Wehrlite, 

clinopyroxenite, and dunite. As mapped, also 

includes minor exposures of layered gabbro 

ecsp	 Round Mountain serpentinite melange— 

Scarce blocks as long as 500 m of basalt, 

diabase, and gabbro (gb), in sheared matrix 

of serpentinized dunite and minor harzburgite. 

Locally includes small intrusive bodies of 

diorite and quartz diorite 

COAST RANGES PROVINCE 

Qls	 Landslide deposits (Holocene and Pleistocene) 

Qg	 Glacial deposits (Pleistocene) 

Pickett Peak terrane—Divided into: 

ppsm South Fork Mountain Schist (Early Cretaceous, 

metamorphic age; protolith age unknown)— 

Intensely crumpled and quartz-veined mica 

schist. Includes large bodies of fine-grained, 

laminated, greenish-bluish metabasalt (mb), 

as well as local metachert (not mapped separately) 

ppv Valentine Spring Formation of Worrall (1981, 

1982) (Early Cretaceous, metamorphic age; 

protolith age unknown)—Dominantly 

metagraywacke of textural zone 2B and 3A 

of Jayko and others (1986). Includes minor 

5
 
amounts of schistose metavolcanic rock (mv) 

and rare metachert (not mapped separately) 

Yolla Bolly terrane—In quadrangle, divided into: 

ybt Taliaferro Metamorphic Complex of Suppe 

(1972) (Early Cretaceous to Middle Jurassic?)—Schistose metagraywacke, crumpled 

phyllite, metagreenstone, and metachert. 

Metachert contains Late Jurassic radiolarians 

at one locality 

ybc Chicago Rock melange (Early Cretaceous to 

Middle Jurassic)—Mostly sheared argillite, 

graywacke, and conglomerate that contains 

very abundant blocks of fine-grained greenstone (gs) and lenses of chert (ch). Also includes scarce serpentinite, rare blueschist, 

and amphibolite knockers (not mapped separately). Radiolarians from chert are Middle 

to Late Jurassic in age. Scarce Buchias are 

of Berriasian and Valanginian ages. Terrain 

commonly characterized by hummocky, 

grass-covered hillsides 

ybh Metagraywacke of Hammerhorn Ridge (Early 

Cretaceous to Middle Jurassic)—Dominantly graywacke that contains lesser amounts 

of argillite and conglomerate, as well as 

abundant lenses of chert (ch) that yields fossils 

of Middle to Late Jurassic age. Includes scarce 

intrusive(?) serpentinite (sp). Generally forms 

resistant ridges and is commonly timber 

covered 

ybd Broken formation of Devils Hole Ridge 

(Early Cretaceous to Middle Jurassic)— 

Dominantly argillite, graywacke, and conglomerate that contains blocks and lenses 

of radiolarian chert (ch) and rare greenstone (not mapped separately) 

KLAMATH MOUNTAINS PROVINCE 

Qls Landslide deposits (Holocene and Pleistocene)—Jumbled gravitationally displaced 

rocks derived from adjacent bedrock 

QTog Older gravel deposits (Pleistocene and (or) 

Pliocene)—Reddish- to yellow-brown, 

moderately well indurated, coarse gravel 

and minor amounts of coarse sand. Clasts 

primarily are well-rounded, light- and darkgray chert but also consist of variable but 

lesser amounts of metavolcanic and 

metasedimentary rocks that are derived 

from Klamath Mountains and Coast Ranges 

provinces 

Ko Overlap assemblage (Early Cretaceous)—Depositional outliers of mudstone, sandstone, and 

conglomerate of Great Valley sequence that 

lie unconformably on basement rocks of 

Klamath Mountains province 

Ksb Shasta Bally batholith (Early Cretaceous)— 

Light-colored, medium-grained, biotitehornblende quartz diorite and granodiorite. 

Potassium-argon and uranium-lead isotopic 

ages of about 136 Ma (Lanphere and others, 

1968; Lanphere and Jones, 1978). Emplacement postdates amalgamation of Klamath 

Mountains terranes. Outcrops generally 

decomposed, producing abundant grus 

Western Klamath terrane—Consists of: 

Smith River subterrane—Divided into: 

srs Metasedimentary rocks (Late Jurassic?)— 

Dark, slaty to phyllitic shale, metagraywacke, 

and minor amounts of stretched-pebble 

conglomerate. Unfossiliferous. Part of 

Galice(?) Formation of Oxfordian to 

Kimmeridgian age 

srv Metavolcanic rocks (Late Jurassic?)— 

Mafic volcanic rocks metamorphosed to lower 

greenschist facies. Shown only as block in 

Round Mountain serpentinite melange of 

Elder Creek terrane 

Hayfork terrane—Consists of: 

Western Hayfork subterrane of Wright (1982) 

(Middle Jurassic)—Units 1, 2, and 3 (wh1, 

wh2, and wh3) combined are equivalent to 

Hayfork Bally Meta-andesite (Irwin, 1977). 

In quadrangle, divided into: 

wh1 Unit 1—Predominantly crystal-lithic tuff 

and tuff breccia of andesitic and basaltic 

composition 

wh2 Unit 2—Predominantly crystal-lithic tuff and 

black slaty argillite 

wh3 Unit 3—Predominantly tuff breccia 

wh4 Unit 4—Volcanogenic sandstone, conglomerate, chert, argillite, quartzose sandstone, 

and crystal-lithic tuff 

whu Undivided part—Small areas of tuff and 

argillite north of Wildwood pluton 

Plutonic rocks—Divided into: 

whpb Basin Gulch pluton (Middle Jurassic)—Dark, medium-grained rocks that vary 

in composition from pyroxene gabbro to 

pyroxene-biotite quartz diorite. Uraniumlead isotopic age of 170 Ma (Wright, 1981). 

Intrudes volcanic rocks of unit 2 (wh2) of 

western Hayfork subterrane and is 

preamalgamation in age 

whpw Walker Point and Wildwood plutons, 

undivided (Middle Jurassic)—Predominantly dark pyroxene gabbro and diorite that 

form outer zone around core of 

clinopyroxenite (cpx). Uranium-lead isotopic 

6
 
age of 169 Ma (Wright, 1981; Fahan, 1982). 

Plutons intrude volcanic rocks of unit 2 (wh2) 

of western Hayfork subterrane and are 

preamalgamation in age 

whpo Oliphant Creek pluton (Jurassic?)—Predominantly biotite-hornblende gabbro. Intrudes volcanic rocks of unit 2 (wh2) of 

western Hayfork subterrane and is 

preamalgamation in age 

whpg Granite (Jurassic?)—Light-colored, 

medium- to coarse-grained leucocratic granite. Intrudes undivided part (whu) of western Hayfork subterrane north of Wildwood 

pluton and probably is preamalgamation 

in age 

eh Eastern Hayfork subterrane of Wright (1981, 

1982) (Middle? Jurassic)—Melange and 

broken formation that includes argillite, 

quartzose sandstone, chert, limestone (ls), 

tuff, and serpentinized ultramafic rocks (sp). 

Limestone locally contains Permian 

(Tethyan?) foraminifers (Irwin and Galanis, 

1976); radiolarians in chert yield both Triassic 

and Jurassic ages (Irwin and others, 1982). 

Unit is generally equivalent to upper unit 

of Hayfork terrane of Irwin (1974) 

Rattlesnake Creek terrane—Divided into: 

rcm Melange (Jurassic and older)—Includes 

serpentinite, pillow basalt, chert, tuff, argillite, and limestone (ls). Northwest of quadrangle, unit includes chert that contains 

Late Triassic to Middle Jurassic radiolarians, as well as limestone that contains late 

Paleozoic fusulinids and Late Triassic 

ammonites and conodonts (Irwin, 1985b; 

Irwin and others, 1985) 

rcds Dike and sill complex (Early Jurassic and 

(or) Late Triassic)—Dominantly diabase, 

diorite, and quartz keratophyre. Uraniumlead isotopic age of 207 Ma measured 

on small segregation of plagiogranite 

(Wright, 1981) 

rcp Plutonic rocks (Early Jurassic and (or) Late 

Triassic)—Gabbro, diorite, quartz diorite, 

and albite granite. Includes Star Mountain 

pluton, which is dominantly leucocratic quartz 

diorite. Uranium-lead isotopic age range of 

193 to 204 Ma (Wright, 1981) 

rcum Ultramafic rocks (age unknown)—Mainly 

serpentinized harzburgite that shows tectonic 

fabric. Includes small bodies of dunite and 

local concentrations of chromite 

North Fork terrane—Divided into: 

nfs Volcanic and sedimentary rocks (Jurassic 

to Permian)—Mafic volcanic and 

volcaniclastic rocks, pillow basalt, thinbedded chert, argillite, conglomerate, 

quartzose sandstone, and rare limestone 

(ls). Chert contains radiolarians of Permian, 

Triassic, and Jurassic ages (Irwin and 

others, 1982) 

nfum Ultramafic rocks (Permian)—Mainly 

serpentinized and sheared harzburgite 

cm Central metamorphic terrane (Devonian, 

metamorphic age)—Undivided wellfoliated hornblende-epidote-albite schist, 

quartz-mica schist, and calc schist. Includes 

Salmon Schist and Abrams Schist (see Irwin, 

1994). Rubidium-strontium isotopic age of 

metamorphism is approximately 380 Ma 

(Lanphere and others, 1968) 

Eastern Klamath terrane—Consists of: 

Redding subterrane—Divided into: 

ekrb Bragdon Formation (Mississippian)— 

Interbedded dark slaty shale and sandstone 

that contains local interbeds of grit and 

stretched-pebble conglomerate rich in chert 

clasts (Murphy and others, 1969) 

ekrc Copley Greenstone (Devonian)—Andesitic to basaltic volcanic rocks that are, in 

quadrangle, metamorphosed to dark-green, 

fine-grained amphibolite and hornfels 

ektr Trinity subterrane (Ordovician)—Mostly 

serpentinized and sheared harzburgite that 

varies in color from light-green to black. 

Locally contains thin veinlets of chrysotile 

INTRODUCTION 

The Red Bluff 30' × 60' quadrangle includes rocks of 

four major geologic provinces: the Klamath Mountains, the 

Coast Ranges, the Great Valley, and the Cascade Range (fig. 

1, on map sheet). These rocks and their geologic histories 

differ greatly from one another. The Klamath Mountains are 

mainly an accumulation of large tectonic slices of oceanic 

crust, upper mantle, and volcanic island arcs that range in 

age from early Paleozoic to Late Jurassic. The rocks of the 

Coast Ranges present in the Red Bluff quadrangle consist of 

oceanic crustal rocks that are somewhat similar lithologically to those of the Klamath Mountains but are Early Jurassic to Cretaceous in age. The Great Valley province includes 

a thick deposit of moderately deformed Jurassic and Cretaceous marine strata that consist of detrital materials derived 

from uplifted basement rocks of the Klamath Mountains and 

the Sierra Nevada. In the western foothills of the Sacramento 

Valley, these strata rest partly on the Coast Range ophiolite 

and partly on the Klamath Mountains basement rocks and 

thus pose a complex tectonic question. In the central part of 

the Sacramento Valley, a mantle of Tertiary and Quaternary 

detrital continental deposits overlies the Great Valley se7
 
quence; these deposits, which are derived from the west, grade 

eastward into coeval volcanic materials derived from the 

Cascade Range province. The stratigraphic and structural 

relations shown on the map provide a key to understanding 

how the rocks of these various provinces were formed and 

were subsequently assembled. 

For the compilation of this geologic map, Irwin is responsible for the rocks of the Klamath Mountains province; 

Blake, Jayko, and Jones, the pre-Cenozoic rocks of the Coast 

Ranges province; Helley, the late Cenozoic deposits of the 

Sacramento Valley; and Harwood, the Cenozoic rocks of the 

Cascade Range province. Previously published geologic 

mapping used in this compilation is summarized in figure 2 

(on map sheet). 

GEOLOGY 

KLAMATH MOUNTAINS PROVINCE 

The northwestern part of the Red Bluff 30' × 60' quadrangle is occupied by a metamorphic-plutonic basement complex of Jurassic and older rocks within the Klamath 

Mountains geologic province. Along the eastern limit of their 

exposure, the Klamath Mountains basement rocks are unconformably overlapped by east- to southeast-dipping, 

unmetamorphosed Cretaceous strata of the Great Valley sequence, which attain a stratigraphic thickness of thousands 

of meters. These Cretaceous strata are also preserved as erosional outliers, some of which cover areas as large as several 

square kilometers, that rest on basement rocks at a few places 

within the Klamath Mountains province. Along the southwestern edge of the province, however, the Klamath Mountains basement rocks are in fault contact with Early 

Cretaceous metamorphic rocks, the South Fork Mountain 

Schist of the Coast Ranges province. 

The basement rocks of the Klamath Mountains province are divided into several allochthonous terranes (Irwin, 

1972, 1977, 1994; Blake and others, 1982). These terranes 

have a general northwesterly trend and are separated by major faults (fig. 3, on map sheet). The terranes consist of rocks 

typical of oceanic crust and island arcs. The joining together 

or amalgamation of the terranes probably occurred sequentially from east to west, as indicated by (1) the progressive 

westward (oceanward) decrease in the ages of ophiolitic parts 

of the terranes, (2) a similar westward younging of the island-arc components, and (3) a general westward younging 

of metamorphic rocks that formed adjacent to the boundary 

faults as a result of the tectonic amalgamation process. Some 

terranes include plutons that are coeval with, and 

magmatically related to, the volcanic rocks that they intrude, 

forming volcano-plutonic pairs (Irwin, 1985a); these plutons, 

which are integral parts of a terrane, intruded their host rocks 

before tectonic transport and subsequent amalgamation of 

the host terrane to another terrane. Examples of such 

preamalgamation plutons in the Red Bluff quadrangle are 

the Wildwood, Walker Point, and other plutons of the western Hayfork subterrane of the Hayfork terrane. In contrast, 

the Shasta Bally batholith, which is the youngest Klamath 

Mountains pluton in the Red Bluff quadrangle, probably intruded during Early Cretaceous time, after all the Klamath 

Mountains terranes had accreted to North America. The general east-to-west succession of Klamath Mountains terranes 

in the Red Bluff quadrangle is the Redding and Trinity 

subterranes of the Eastern Klamath terrane, the Central metamorphic terrane, the North Fork terrane, the eastern and 

western Hayfork subterranes of the Hayfork terrane, the 

Rattlesnake Creek terrane, and the Smith River subterrane 

of the Western Klamath terrane (fig. 3, on map sheet). 

The Redding subterrane is present in the Red Bluff quadrangle only as a small (about 2 km2) structural outlier of the 

Bragdon Formation and as a narrow southern extension of 

metamorphosed rocks belonging to the Copley Greenstone. 

The outlier of the Bragdon Formation, which here consists 

of slaty sandstone and shale, is inferred to have been thrust 

onto the Central metamorphic terrane along a fault that locally contains slices of serpentinite. The serpentinite presumably was derived from the nearby Trinity subterrane, which 

in the Red Bluff quadrangle consists entirely of serpentinized 

ultramafic rocks. The Central metamorphic terrane, which is 

separated from the Trinity subterrane by the Bully Choop 

Thrust Fault, includes two Devonian formations, the Abrams 

Schist and the Salmon Schist, which have not been mapped 

separately herein. 

The North Fork terrane, which is separated from the 

Central metamorphic terrane by the Siskiyou Thrust Fault, 

consists of metavolcanic and metasedimentary rocks that have 

ophiolitic rocks at their base. In the Red Bluff quadrangle, 

the ophiolitic rocks of the North Fork terrane, which include 

ultramafic rocks, gabbro, and diabase, are highly attenuated 

compared to the more northerly reaches of the terrane, where 

they form a belt as much as several kilometers wide (Ando 

and others, 1983). The ophiolitic rocks are presumably Permian in age, and their overlying strata contain lenses of radiolarian chert that ranges in age from Permian to Jurassic 

(Blome and Irwin, 1983). North of the Red Bluff quadrangle, 

a few lenses of limestone in the North Fork terrane contain a 

Schwagerinid fusulinid fauna of Late Pennsylvanian or Early 

Permian age. The part of the North Fork terrane that lies 

south of the Trinity–Shasta County line has been mapped 

only in reconnaissance. 

The Hayfork terrane lies west of the North Fork terrane, from which it is separated by the North Fork Thrust 

Fault. In the Red Bluff quadrangle, the Hayfork terrane is 

subdivided into two subterranes, the eastern Hayfork and 

western Hayfork subterranes, which are separated by the eastdipping Wilson Point Thrust Fault (Wright, 1982). 

The eastern Hayfork subterrane is a melange and broken formation that occupies a zone about 9 km wide along 

the southwest side of the North Fork terrane. It mostly consists of sheared argillite, chert, and other metasedimentary 

8
 
and metavolcanic rocks but also contains scattered blocks of 

limestone and rare blocks of amphibolite. The chert is commonly Triassic in age but at one locality is Permian; however, no unequivocally Jurassic chert has been identified 

(Blome and Irwin, 1983). Some limestone of the eastern 

Hayfork subterrane contains late Late Permian fusulinids of 

Tethyan faunal affinity (Nestell and others, 1981). These 

fusulinids are younger than, and are faunally distinct from, 

the fusulinids of the adjacent North Fork terrane. 

The western Hayfork subterrane in the Red Bluff quadrangle consists mainly of the Hayfork Bally Meta-andesite 

and the Wildwood, Walker Point, and other related plutons. 

The Hayfork Bally Meta-andesite is a thick, coherent sequence of volcaniclastic strata and lesser amounts of 

interbedded argillite and chert; in the Red Bluff quadrangle, 

it has been divided into four informal stratigraphic subunits 

(Wright, 1981). It was intruded by the preamalgamation Wildwood and other cogenetic plutons about 170 Ma and represents a remnant of a volcanic arc of Middle Jurassic age. 

The Rattlesnake Creek terrane is a melange, largely 

ophiolitic, that is found along the southwest side of the Western Hayfork subterrane; the terranes are separated by the Salt 

Creek Fault. The melange includes thin-bedded chert that 

contains Late Triassic to Middle Jurassic radiolarians, as well 

as blocks of limestone that yields both late Paleozoic 

fusulinids and Late Triassic ammonites and conodonts. Large 

units mapped separately within the melange in the Red Bluff 

quadrangle include a serpentinized peridotite body, which 

crops out in an area of about 30 square kilometers, and the 

preamalgamation(?) Star Mountain pluton of presumed Early 

Jurassic age (Wright, 1981; Irwin, 1985a). 

The Western Klamath terrane has been divided into several subterranes (Blake and others, 1982); one of these is the 

Smith River subterrane, which forms a nearly continuous belt 

along the western border of the central and southern parts of 

the Klamath Mountains province. In the Red Bluff quadrangle, the Smith River subterrane consists of slaty shale and 

sandstone of the Galice(?) Formation; it crops out as discontinuous, relatively narrow fault slices that separate rocks of 

the Rattlesnake Creek terrane from those of the Coast Ranges. 

In the southernmost part of the Klamath Mountains, smaller, 

fault-bounded slices of the Smith River subterrane are found 

along the boundary between the Coast Ranges and Great 

Valley provinces. The significance of these slices will be discussed later. 

In the Red Bluff quadrangle, the Great Valley sequence 

is mapped both as an overlap assemblage of Cretaceous strata 

and as part of the Elder Creek terrane of Jurassic and Cretaceous strata. The lower part of the overlap assemblage lies 

unconformably on the Klamath Mountains basement rocks 

north of the Cold Fork Fault Zone, while its upper part is 

thought to lie unconformably on the youngest strata of the 

Elder Creek terrane south of the fault zone. The oldest known 

fossil from the overlap assemblage in the Red Bluff quadrangle is Hauterivian in age, although slightly older fossils 

of late Valanginian age are known from the Glade Creek 

outlier about 20 km west of the quadrangle (Jones and Irwin, 

1971). The overlap assemblage clearly marks the end of the 

Nevadan orogeny; however, it has been involved in several 

subsequent tectonic events, as described in the following 

sections. 

COAST RANGES PROVINCE 

The Franciscan Complex of the Coast Ranges has been 

divided into the Pickett Peak and Yolla Bolly terranes. Within 

the structurally higher Pickett Peak terrane, two distinctive 

units have been mapped, the South Fork Mountain Schist 

and the Valentine Spring Formation of Worrall (1981). These 

two units are believed to have been metamorphosed during 

the same event, although they are now separated by the Log 

Springs Thrust Fault. 

The Yolla Bolly terrane has been subdivided into four 

tectonic units that are separated by thrust faults. The units 

are identified by differences in lithology and metamorphic 

grade. The structurally highest unit is the Taliaferro Metamorphic Complex of Suppe (1973), which consists of 

jadeite-bearing metagraywacke of textural zone 2B (Jayko 

and Blake, 1989), metachert, and metavolcanic rocks, the 

latter two of which contain distinctive blue amphibole. The 

structural state varies from coherent in the north to melange 

near Oven Lid, where the rocks have been structurally mixed 

with those of the underlying (informally named) Chicago 

Rock melange (Jayko and Blake, 1986). The contact with 

the overlying Valentine Spring Formation is sharply defined 

and has been mapped as the Sulphur Creek Thrust Fault 

(Worrall, 1981) on the basis of both metamorphic and structural discontinuities. 

The second-highest unit, the Chicago Rock melange, 

also varies from relatively coherent broken formation to rather 

chaotic melange and contains abundant blocks of greenstone 

(most of which are too small to map at this scale) and lenses 

of chert, as well as rare knockers of blueschist and sparse 

intrusive serpentinite. The upper contact with the Valentine 

Spring Formation is, in most places, the Sulphur Creek Thrust 

Fault; however, in the southern part of the quadrangle, a tectonic slice of the Taliaferro Metamorphic Complex is present 

between these two units. 

The third unit, the metagraywacke of Hammerhorn 

Ridge (Jayko and Blake, 1986), contains more coherent beds 

of graywacke and chert and less volcanic rock than any of 

the other units of the Yolla Bolly terrane. The upper contact 

has been placed at the top of the coherent sequence and is 

inferred to be a thrust fault, the Chicago Camp Thrust Fault, 

although the thrust movement probably was distributed 

throughout the overlying Chicago Rock melange. 

The structurally lowest unit, the broken formation of 

Devils Hole Ridge (Jayko and Blake, 1986), is somewhat 

similar lithologically to the Chicago Rock melange but is 

usually more coherent and contains fewer blocks of green9
 
stone and chert. West of the Red Bluff quadrangle, however, 

these two units are difficult to differentiate except where the 

metagraywacke of Hammerhorn Ridge intervenes. The upper contact of the Devils Hole Ridge unit is locally marked 

by sheared serpentinite and has been mapped at the base of 

the coherent Hammerhorn Ridge unit. The presence of Early 

Cretaceous Buchia in the Devils Hole Ridge unit below Late 

Jurassic radiolarians in the overlying Hammerhorn Ridge unit 

requires a thrust fault. However, not one of the units of the 

Yolla Bolly terrane is as stratally disrupted as the melange 

of the Central Franciscan belt (Blake and others, 1988), which 

lies west of the Red Bluff quadrangle. 

All four units of the Yolla Bolly terrane contain lenses 

of radiolarian chert that were originally thought to be 

interbeds. Later work (Isozaki and Blake, 1994) has demonstrated, however, that these chert lenses are separated 

from the underlying clastic metasedimentary rocks by 

knife-sharp, bedding-parallel faults, which probably 

formed during subduction-related thrusting. 

The rocks of the Pickett Peak and Yolla Bolly terranes 

formerly were thought to have been metamorphosed during 

the same Cretaceous event (Blake and others, 1967); however, more recent work (Jayko and others, 1986; Jayko and 

Blake, 1989) indicates that (1) a progressive eastwardly increase in textural and metamorphic grade is present in each 

terrane, (2) rocks of the Pickett Peak terrane contain early 

deformational-metamorphic structures not seen in the rocks 

of the Yolla Bolly terrane, and (3) a major thrust fault, the 

Sulphur Creek Thrust Fault of Worrall (1981), separates the 

two terranes. These features suggest the possibility of two 

separate metamorphic events. Although the exact timing of 

the two events is not clear, the regional geologic relation, as 

well as available radiometric and fossil data, suggest that 

both events occurred during the Cretaceous. 

Along the west side of the Sacramento Valley south of 

the Cold Fork Fault Zone, Late Jurassic and Early Cretaceous strata of the Great Valley sequence are exposed on the 

steeply dipping western limb of a large syncline. Within the 

Red Bluff quadrangle, these strata are in fault contact with 

ultramafic rocks of the Coast Range ophiolite; however, 8 

kilometers south of the quadrangle along the South Fork of 

Elder Creek, the basal Late Jurassic sedimentary rocks of 

the Great Valley sequence are in depositional contact with 

the underlying mafic breccia that marks the top of the 

ophiolite. The ophiolite is thought to represent oceanic crust 

and upper mantle upon which the Late Jurassic strata were 

deposited. The ophiolite and the overlying Jurassic and Early 

Cretaceous sedimentary rocks have been named collectively 

the Elder Creek terrane (Blake and others, 1982). 

Although previously considered to be an older part of 

the overlap assemblage that rests unconformably on Klamath 

Mountains basement rocks to the north, the oldest sedimentary strata of the Elder Creek terrane are clearly not part of 

the overlap assemblage but were deposited during the Nevadan orogeny (Jones and others, 1969). This was further discussed by Suppe (1973), who proposed that the “oceanic” 

Great Valley sequence is presumably allochthonous with respect to North America and that a major fault (subduction 

zone) lies hidden beneath the Cretaceous cover rocks of the 

Great Valley sequence. Because of renewed movement on 

all of the fault zones and a lack of sedimentological studies 

tied to the stratigraphy, the timing of stratal continuity is not 

clear. We have therefore arbitrarily placed the contact at the 

base of the Turonian-age Venado Sandstone (Durham, 1962; 

see also, Kirby, 1943) (not shown separately on map) because these are the oldest rocks that lie in depositional contact on Sierran basement, as shown in drill holes to the east. 

SACRAMENTO VALLEY AND CASCADE RANGE
 

PROVINCES
 

The eastern two-thirds of the Red Bluff quadrangle contains low-rolling topography that slopes toward the Sacramento River, the largest drainage system in northern 

California. This part of the quadrangle is underlain by late 

Cenozoic sedimentary and volcanic rocks that rest with 

marked unconformity on both the Late Cretaceous rocks of 

the Great Valley sequence and locally on the Shasta Bally 

batholith about 6.5 km northwest of Cloverdale. 

The western part of the Sacramento Valley is underlain 

by Pliocene continental deposits of the Tehama Formation, 

and the eastern part is underlain by coeval volcanic rocks of 

the Tuscan Formation. The Nomlaki Tuff Member, which 

is present locally at or near the base of both the Tehama 

and Tuscan Formations, blanketed much of the northern 

Sacramento Valley about 3.4 Ma, approximately the time 

of major Neogene uplift and erosion of the Coast Ranges 

province. In the west, continental deposits of the Tehama 

Formation accumulated in coalescing alluvial fans along 

the eastern margin of the rising Coast Ranges. To the east, 

lahar deposits and minor lava flows, which are composed of 

basalt and basaltic andesite, flowed westward from several 

volcanic centers near Lassen Peak, 35 km east of the quadrangle at the southern end of the Cascade Range, forming 

the Tuscan Formation. Rocks of the Tehama and Tuscan Formations interfinger in a zone several kilometers wide near 

the present-day channel of the Sacramento River, which we 

have taken arbitrarily as the formation boundary. 

The Tehama and Tuscan Formations were beveled and 

capped by the Red Bluff Formation, a thin unit of brightred gravel in a red sandy matrix. The Red Bluff Formation generally forms the highest part of the valley 

landscape west of the Sacramento River, where it is found 

as remnants of a highly dissected and eroded geomorphic 

surface (Helley and Jaworowski, 1985). We interpret the 

Red Bluff Formation to be a sedimentary cover on a pediment surface because (1) the Red Bluff apparently was 

deposited on a cut surface of low relief that extends regionally across various older rock types, (2) the deposits 

are thin and locally derived, and (3) the coarse, poorly 

10
 
sorted gravel was deposited by a very different flow regime than the one that deposited the underlying finegrained sediment of the Tehama Formation. The pediment 

and the gravels of the Red Bluff Formation apparently 

formed during a period of lateral planation by highgradient streams when impeded drainage on the Sacramento River raised local base level. Well-developed, 

noncalcic, brown soils (Xeralfs) of the Redding and Corning Soil Series characterize the Red Bluff Formation. 

On the west side of the Sacramento Valley, all units 

younger than the Red Bluff are found in nested terraces usually tens of meters below the pediment surface; this depositional scheme is also partially developed on the east side of 

the valley, but, locally, younger alluvial deposits and volcanic rocks extend over the Red Bluff surface (Helley and others, 1981). Four such Pleistocene terrace deposits have been 

recognized on the west side of the Sacramento Valley; they 

have been correlated with the Riverbank and Modesto Formations of the San Joaquin Valley to the south (Marchand 

and Allwardt, 1981) on the basis of radiometric ages, soilprofile development, geomorphic expression, and superposition. In the Red Bluff quadrangle, the Riverbank and 

Modesto Formations are divided into informal upper and 

lower members. Original alluvial materials on the terraces 

on the west side of the valley are virtually identical lithologically, but each deposit has a characteristic elevation, degree of dissection, and amount of soil-profile development, 

each of which are chiefly a function of age. Terrace deposits 

on the east side of the Sacramento Valley are lithologically 

indistinguishable from each other, but the presence of volcanic debris readily distinguishes them from deposits on the 

west side of the valley. Correlation of east-side terrace deposits is based on the same criteria used to correlate the westside terrace deposits. Within the Pleistocene deposits, the 

greatest elevation difference exists between the top of the 

Red Bluff Formation and the highest terrace of the Riverbank 

Formation, the oldest Pleistocene terrace. Streams throughout the Sacramento Valley had incised their valleys tens of 

meters during the time between deposition of the Red Bluff 

and deposition of the lower member of the Riverbank, which 

suggests a major regional lowering of base level. The difference in terrace elevation between the lower and upper members of the Riverbank and the lower and upper members of 

the Modesto, however, is only a few meters. 

Terrace deposits of Riverbank age are well developed 

and have been best preserved in the Sacramento Valley west 

of Anderson, near Balls Ferry, and along Cottonwood Creek 

and its tributaries. Riverbank-age deposits also are present 

along the west side of the Sacramento River south of the city 

of Red Bluff, as well as along Pine Creek, Reeds Creek, Red 

Bank Creek, Oat Creek, and Elder Creek. The terrace deposits along these streams merge eastward to form a broad terrace plain along the west bank of the Sacramento River, which 

extends from the city of Red Bluff south to the quadrangle 

boundary and beyond. In contrast to the west side, the east 

side of the valley displays fewer terraces and more erosional 

morphology. 

Deposits of Modesto age are best preserved in the same 

areas as those of Riverbank age. The Riverbank and Modesto 

deposits clearly were laid down by the same watercourses 

that exist today; however, the volume of Holocene deposits 

that are accumulating at present in open, nonvegetated, 

sediment-filled channels along the Sacramento River and 

its tributaries commonly is significantly smaller than the 

volume of material in Modesto, Riverbank, and older deposits. 

TECTONIC HISTORY 

The oldest tectonic event recorded in the rocks of the 

Red Bluff quadrangle is the metamorphism that formed the 

Abrams Schist and the Salmon Schist of the Central metamorphic terrane in the Klamath Mountains province. The 

metamorphism occurred during Devonian time (Lanphere and 

others, 1968) when volcanic and sedimentary protoliths of 

the Central metamorphic terrane were overridden by rocks 

of the Trinity subterrane along the Bully Choop Thrust Fault. 

This subduction event may be related to the arc volcanism 

that resulted in the formation of the Copley Greenstone and 

other Devonian volcanic rocks of the overlying Redding 

subterrane. 

The terranes west of the Central metamorphic terrane— 

the North Fork, Hayfork, and Rattlesnake Creek terranes, as 

well as the Smith River subterrane of the Western Klamath 

terrane—were joined during a sequence of Middle and Late 

Jurassic events. The timing of these events is based on the 

ages of the youngest rocks in the terranes and on the Middle 

Jurassic to Early Cretaceous ages of the postamalgamation 

plutons that crosscut the terrane boundaries. Suturing of the 

westernmost rocks, the Smith River subterrane, took place 

in Late Jurassic time on the basis of potassium-argon isotopic ages of about 150 Ma for the regional metamorphism of 

the Galice Formation (Lanphere and others, 1978). This 

metamorphic event probably represents part of the Nevadan 

orogeny. 

The postamalgamation plutons are thought to result from 

a subduction process in which rocks of the downgoing slab 

are melted and then injected into the upper-plate terrane(s). 

Nearly all the postamalgamation plutons crop out north of 

the Red Bluff quadrangle. The Shasta Bally batholith, which 

intruded the Redding and Trinity subterranes during Early 

Cretaceous time, about 136 Ma (Lanphere and others, 1968; 

Lanphere and Jones, 1978), is the only significant 

postamalgamation pluton in the quadrangle. 

Paleomagnetic study of the Klamath Mountains by 

Mankinen and others (1989) indicated that the Permian and 

Triassic rocks of the Redding subterrane have rotated clockwise approximately 106° relative to stable North America 

and that the Jurassic rocks have rotated clockwise approximately 60°. In addition, no paleomagnetic evidence was 

11
 
 

found for significant latitudinal displacement of the Klamath 

Mountains terranes relative to North America. Evidence from 

the Shasta Bally batholith indicates that major rotation virtually ceased in Early Cretaceous time when the batholith 

was emplaced and that, after a hiatus of about 100 m.y., during which time the Cretaceous overlap assemblage was deposited, minor rotation of the Klamath Mountains occurred 

as a result of extension of the Basin and Range province. 

The emplacement of the Shasta Bally batholith and the virtual cessation in its rotation probably mark the time of accretion of the amalgamated Klamath Mountains terranes to 

the North American continent. 

Near Greasewood Hill in the southwestern part of the 

quadrangle, the Klamath Mountains, the Cretaceous overlap 

assemblage, the Elder Creek terrane, and the Coast Ranges 

join one another to form the Yolla Bolly junction (fig. 3, on 

map sheet; see also, Blake and Jones, 1977, 1981). The events 

that led to the formation of this junction are still not clearly 

understood despite the fact that rock distribution and age are 

fairly well known. Despite the uncertainties, we surmise that 

the formation of the Yolla Bolly junction probably involved 

the following sequence of events:

 (1) The obduction of the Coast Range ophiolite and the 

lower part of the Great Valley sequence, both of which 

are part of the Elder Creek terrane, onto a Late Jurassic 

volcanic arc, the Smith River subterrane of the Western 

Klamath terrane, as suggested by the presence of slices 

of the Smith River subterrane along the western margin 

of the Coast Range ophiolite, both in the quadrangle and 

at least as far south as Elk Creek, 8 km south of the quadrangle in the Willows 30' × 60' quadrangle (Jayko and 

Blake, 1986); the timing of this event could be as old as 

the Nevadan orogeny (Late Jurassic, approximately 150 

Ma) or as young as Early Cretaceous.

 (2) The accretion (subduction) of both the Pickett Peak 

and Yolla Bolly terranes, probably during two different 

events, beneath the now-composite Klamath Mountains– 

Elder Creek terrane.

 (3) The attenuation of the Elder Creek terrane by lowangle normal faulting along the Beehive Flat Fault, 3 km 

south of the quadrangle, as well as the formation of the 

Round Mountain serpentinite melange; these events probably commenced during subduction of lower-plate rocks 

and may have continued until earliest Tertiary time (Jayko 

and others, 1987).

 (4) The westward thrusting of the Elder Creek terrane, which was accompanied by left-lateral tear faulting along the Cold Fork and Elder Creek Fault Zones 

(Glen, 1990); this thrusting may be a manifestation of 

westward thrusting of the entire Klamath Mountains 

over the Elder Creek terrane and the Franciscan Complex (Blake and others, 1993), and, although the timing of this event is poorly constrained in the quadrangle, 

farther north in southwestern Oregon the overthrusting 

of the Klamath Mountains onto the Franciscan Complex is known to have occurred between about 58 and 

52 Ma (Roure and others, 1986).

 (5) The formation of the Coast Range Fault, the high-angle 

reverse fault that forms the present eastern and northern 

boundary of the Franciscan Complex (Jayko and others, 

1987). 

The timing of the onset of faulting along the Coast Range 

Fault, which was partly responsible for the uplift of the previously accreted Franciscan rocks, is not clear, but the uplift 

may have commenced about when the Nomlaki Tuff Member was erupted (3.4 Ma), because abundant Franciscan detritus first appears above that horizon in the Tehama 

Formation. Faulting probably continued throughout the time 

of deposition of the Red Bluff Formation and may even be 

active today: an earthquake swarm of more than ten events 

occurred near this fault from March 22 through April 4, 1982 

(Jeff Howard, California Department of Water Resources, 

written commun., 1983). 

Pliocene and younger deposits in the Sacramento Valley and eastern foothills show evidence of deformation that 

has occurred within the past 2.5 m.y. (Harwood, 1984; 

Helley and Jaworowski, 1985; Harwood and Helley, 1987). 

In the eastern part of the Red Bluff quadrangle, the orientation and age of late Cenozoic structures differs significantly 

north and south of the Red Bluff Fault. South of the Red 

Bluff Fault, major late Cenozoic structures strike north or 

north-northwest and were formed between 1.0 and 2.5 Ma. 

North of the Red Bluff Fault, however, late Cenozoic structures strike east-northeast and were formed less than 1.0 

m.y. ago. 

The northwest-trending zone of short fault segments located southeast of the city of Red Bluff marks the northern 

half of the Chico Monocline (Harwood and others, 1981). 

The monocline is a southwest-facing flexure that drapes the 

Tuscan Formation and underlying rocks over a steeply east 

dipping, high-angle reverse fault, which offsets metamorphic 

basement rocks about 400 m up-to-the-east (Harwood and 

Helley, 1987). The monocline was formed between 1.0 and 

2.5 Ma under the essentially east-west compressive stress 

that steeply thrust up the Sierran block east of the Sacramento Valley along a Mesozoic fault in the basement rocks 

(Harwood, 1984; Harwood and Helley, 1987). Although evidence for lateral movement during formation of the monocline is scarce, limited slickenside data suggest minor 

left-lateral slip (Harwood and others, 1981). 

The north-trending Corning Fault, which lies west of 

the Chico Monocline, has no surface expression in the Sacramento Valley but is defined by seismic reflection data 

(Harwood, 1984; Harwood and Helley, 1987), which indicate a moderately steep, eastward dip and reverse, east-sideup movement. Upward and westward movement of the 

hanging wall of the fault deformed the Tehema and Red Bluff 

Formations into the north-trending Corning Domes, which 

have surface expression just south of the Red Bluff quadrangle (Helley and Jaworowski, 1985; Harwood and Helley, 

12
 
1987). The Los Molinos Syncline lies between the Corning 

Fault and the Chico Monocline and forms a north-northwesttrending trough that locally controls the position of the Sacramento River. 

The change from north- or northwest-striking structures 

to east-northeast-striking structures occurs at the Red Bluff 

Fault, which strikes about N. 60° E. diagonally across the 

valley subsurface and passes beneath the city of Red Bluff. 

Southwest of Red Bluff, the fault has no surface expression, but, 

northeast of the city, Pliocene volcanic rocks of the Tuscan Formation and the older gravel deposits of unit QTog are folded into a 

northeast-trending, southwest-plunging anticline and three 

small domal structures along the extended trend of the Red 

Bluff Fault. As far as can be determined from data available, 

the Red Bluff Fault appears to have normal, down-to-the-south, 

late Cenozoic displacement that offsets the base of the Pliocene 

rocks by folding and (or) faulting about 140 m. Griscom (1973) 

inferred major right-lateral slip on the Red Bluff Fault from 

tentative correlation of offset magnetic and gravity anomalies 

associated with basement rocks beneath the northern part of 

the Sacramento Valley. No indication of major late Cenozoic 

lateral movement exists, but earlier strike-slip displacement 

cannot be ruled out. 

About 25 km north of Red Bluff, rocks east of the Sacramento River are offset up-to-the-north along the Battle 

Creek Fault Zone. The amount of displacement on the fault 

and the height of the prominent fault scarp along Battle Creek 

increases significantly toward the east (Harwood and others, 

1980; Harwood and Helley, 1987). West of the Sacramento 

River, the straight channel and valley of Cottonwood Creek 

is on strike with the Battle Creek Fault Zone and may, in 

part, coincide with the western extension of the fault. The 

most likely projection of the Battle Creek Fault Zone is down 

the South Fork of Cottonwood Creek where many linear features are found within and surrounding Quaternary terraces 

(Helley and others, 1981). 

Although the Battle Creek Fault Zone offsets a number 

of older volcanic flows and its scarp is buried or draped by 

younger volcanic units, the movement history and slip rate 

of the fault are not well known. Many of the volcanic units 

are high-alumina basalts, which are extremely low in K2O 

and cannot be dated accurately by the potassium-argon 

method. If the volcanic fanglomerate, which is offset by the 

fault near the confluence of Battle Creek and the Sacramento 

River, correlates with the Red Bluff Formation as proposed 

herein, major down-to-the-south, normal faulting occurred 

less than 1 million years ago. The Battle Creek Fault scarp 

apparently channeled the ash flow that formed the 0.4–Ma 

Rockland ash bed of Sarna-Wojcicki and others (1982) during its emplacement. Thus, major movement on the fault may 

have occurred between about 0.4 and 1.0 Ma. 

Between the Battle Creek and Red Bluff Faults, the 

major meanders of the Sacramento River are controlled by 

southwest-plunging folds that are referred to as the Inks Creek 

Fold System (Helley and others, 1981; Harwood, 1984; 

Harwood and Helley, 1987). The trace of the anticline in the 

fold system extends northeastward from the river east of Juniper Point and merges with the Battle Creek Fault Zone near 

the quadrangle boundary; the synclinal trace approximately 

coincides with Inks Creek. West of the river, between Table 

Mountain and Hooker, the Pliocene Tehama Formation is 

arched into the Hooker Dome, which is shown clearly by the 

drainage pattern of Hooker Creek and Blue Tent Creek. 

Deformation that produced both the Inks Creek Fold System 

and the Hooker Dome began shortly before eruption of the 

Rockland ash bed, which rests unconformably across the 

eroded contact between the Red Bluff Formation and Tehama 

Formation at Round Mountain, about 2 km south of Juniper 

Point. Early phases of folding probably accompanied early 

movement on the Battle Creek Fault. Subsequent folding and 

doming produced the incised meanders of the Sacramento 

River and deformed the Quaternary terrace deposits on the 

north side of Hooker Dome, which may be as young as 

250,000 yr B.P. 

The kinematic relations, if any, between late Cenozoic 

structures in the northern part of the Sacramento Valley and 

those in the provinces to the west are unknown. We speculate, however, that the east-northeast-striking Battle Creek 

Fault Zone may extend southwestward under the South Fork 

of Cottonwood Creek to join the Oak Flat and Sulphur Spring 

Faults near the Yolla Bolly junction. Late Cenozoic movement on the Battle Creek Fault certainly has been predominantly south-side-down normal faulting, but little 

evidence is available on pre-late Cenozoic movement. The 

northeast-striking Bear Creek, Battle Creek, and Red Bluff 

Faults possibly reflect a broad zone of preNeogene left-lateral displacement, which accommodated 

movement during early Cenozoic clockwise rotations of 

the Klamath Mountains and the Oregon Coast Ranges 

(Magill and Cox, 1981). 

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15