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F01

EASTERN 

RATTLESNAKE

 CREEK

 TERRANE

IRONSIDE

 MOUNTAIN

 BATHOLITH

WEAVERVILLE FORMATION

WESTERN

HAYFORK

TERRANE

WESTERN 

HAYFORK

TERRANE

WH

 (Tertiary postaccretion overl

123°15' 123°10' 

40°45'

40°40'

40°35'

40°30'

 

GENERALIZED T

The oldest rocks in the Hayfork 15' quadrangle, present al

Mountain outlier of the Eastern Klamath terrane, which is 

15' quadrangle. There, these Mississippian(?) or older rock

of the Central Metamorphic terrane by ultramafic rocks of 

however, only one small remnant of Trinity ophiolite (Oum

Metamorphic terrane is in fault contact with the North For

much of its western side that is thrust westward over the E

also a melange, occupies much of the central part of the qu

the underlying Western Hayfork terrane, based on interpre

terrane (WHT) as antiformal windows. The Western Hayfo

genetically related to the Ironside Mountain batholith.

Base: U.S. Geological Survey Hayfork 15-minute 

quadrangle, 1951; polyconic projection,

North American Datum 1927.

Reconnaissance Geologic Map of the Hayfork 15’ Quadrangle, Trinity County, California

By

William P. Irwin

2010

CONTOUR INTERVAL 50 FEET

DATUM IS MEAN SEA LEVEL

AREA

OF MAP CALIFORNIA

19O

magnetic north

true north

Geology mapped by W.P. Irwin in 1968-72; 

assisted by A.W. Snoke,1968, and Andrew 

Tarshis,1970. GIS database and digital cartography by W.P. Irwin and C.M. Wentworth, 2009 

Edited by T.A. Lindquist

Manuscript approved for publication March 2, 2010

Contact, showing dip; dashed where approximately located

Fault, showing dip; dashed where approximately located; 

 teeth on upper plate where thrust

Small fold, showing plunge of axis where known

Attitude of inclined bedding

Inclined Vertical Horizontal

 Attitude of foliation

 Inclined Vertical 

 Attitude of joints 

Mine adit 

50

30

40

20

30

Inclined Vertical Horizontal

 Attitude of cleavage

MAP SYMBOLS

10

F15

Fossil locality

30

Prospect pit

Direction and dip of bedding

40°30'

123°15' 123°10' 123°05'

40°40'

40°35'

123°00'

40°30'

40°35'

40°40'

R. 12 W. R. 11 W. R. 10 W.

T. 31 N.

T. 32 N.

T. 33 N.

T. 33 N. 

T. 32 N. 

T. 31 N. 

 Table 1. Fossil localities in the Hayfork 15' quadrangle 

 Map# I&B#(1) Field# Lithology Fossils Age 

 

 F01 197 I-1-72 Limestone Fusulinids Early Permian

 F02 198 I-22-81 Chert Radiolarians Middle to Late Jurassic

 F03 93 I-14-77 Chert Radiolarians Triassic or Jurassic

 F04 94 I-32-70 Limestone Fusulinids Early Permian

 F05 95 I-1-73 Limestone Foraminifers Pennsylvanian

 and gastropods or Permian

 F06 96 I-49-70 Limestone Conodonts Ordovician to Triassic

 F07 97 I-11-70 Limestone Conodonts Late Triassic

 F08 98 I-15-70 Limestone Conodonts Ordovician to Triassic

 F09 99 I-11-76 Chert Radiolarians Middle or Late Triassic

 F10 200 W-57-28c Limestone Fusulinids Late Pennsylvanian

 to early Permian 

 F11 201 I-3-76 Chert Radiolarians Early or Middle Jurassic 

 F12 202 I-10-76 Chert Radiolarians Early or Middle Jurassic 

 F13 203 I-1-76 Chert Radiolarians Early Jurassic 

 F14 I-11-69 Great Valley seq. Foraminifers Early Cretaceous (late 

 Albian?)(2) 

 F15 99 I-19-70 Limestone Conodonts Middle Triassic 

 F16 100 I-10-72 Limestone Conodonts Early Triassic

 F17 101 I-26-81 Chert Radiolarians Permian

 I-8-82 Chert Radiolarians Permian

 F18 102 I-32-68 Conglomerate Rugose corals Silurian 

 I-18-70 Conglomerate Mixed faunas Permian

 F19 103 I-10-68 Limestone Microfauna Permian or early

 Mesozoic

 (1) I&B# refers to numbers from Irwin and Blome (2004).

 (2) Age by W.V. Sliter, written commun., 1974.

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GREAT VALLEY OVERLAP ASSEMBLAGE

Major unconformity, Early Cretaceous (~136 Ma)

TECTONOSTRATIGRAPHIC TERRANES

WEAVERVILLE FORMATION

 Western

 Hayfork

 Eastern

 Hayfork

North Fork Central 

Metamorphic

 Eastern

Klamath

Rattlesnake

 Creek

Lower Cretaceous

 (Hauterivian)

Miocene and

(or) Oligocene

TERTIARY

CRETACEOUS

JURASSIC

TRIASSIC

PERMIAN

MISSISSIPPIAN

DEVONIAN

ORDOVICIAN

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 Alluvium (Holocene and Pleistocene)––Unconsolidated sand and gravel in channels of modern streams and on 

 associated low terraces. Much has been reworked by placer mining for gold. Includes some deposits that result 

 from slumping and slope wash in areas underlain by Weaverville Formation. Structural symbols in unit Qal

 were measured on small outcrops of underlying bedrock 

 Terrace deposits (Quaternary)––Moderate- to high-level terraces, generally but not everywhere covered by a veneer 

 of sand and gravel. Includes associated colluvium. Terraces from which the sand and gravel have been mostly 

 removed from bedrock by gold-placer mining are shown as unit Qtm 

 Landslide deposits (Quaternary and older?) 

BEDROCK

 Weaverville Formation (Miocene and (or) Oligocene)—Nonmarine, weakly consolidated mudstone, sandstone, and 

 conglomerate, containing impervious dark-green clay and sparse interbeds of light-colored tuff. Locally contains 

 abundant fossil plants and some lignitic coal beds. The fossil plants are considered Oligocene(?) (MacGinitie, 1937); 

 the pollen and spores are considered late Oligocene and (or) early Miocene (Barnett, 1982). Formation is poorly 

 exposed, mainly owing to weak consolidation. Distribution and contact relations shown on map are based in large 

 part on interpretation of topography

 GREAT VALLEY OVERLAP ASSEMBLAGE

Great Valley sequence (Lower Cretaceous)—Firmly consolidated and well-bedded marine mudstone, sandstone, and 

 conglomerate. Small patch at Summit Creek is mostly mudstone that has sparse calcareous nodules. Patch near 

 center of southern boundary of the quadrangle is mostly conglomerate. Microfossils from patch at southeast corner 

 of quadrangle (but collected just east of the quadrangle boundary) are considered (K.D. Berry, written commun., 

 1969) to be Early Cretaceous (Hauterivian-Barremian, Zone K). Microfossils from the Summit Creek patch (fossil 

 locality no. 14; table 1) are probably late Early Cretaceous (Albian) (W.V. Sliter, written commun., 1974) 

TECTONOSTRATIGRAPHIC TERRANES

Bragdon(?) Formation (Mississippian)—Well-indurated conglomerate, grit, sandstone, thin-bedded chert and, 

 locally, recrystallized limestone (ls, where divided). Includes minor(?) amounts of mafic volcanic rock, 

 some of which is vesicular and weathers purple. Part of thrust plate, the Oregon Mountain outlier, which 

 structurally overlies rocks of Central Metamorphic terrane (see Irwin, 2009). Correlation with the Bragdon 

 Formation is uncertain. May be correlative with units of Yreka terrane (Cashman and Cashman, 2006)

Abrams Mica Schist (Devonian)––Schistose metasedimentary rocks, generally micaceous and quartzitic. 

 Contains micaceous marble, most commonly as small lenses near base of unit. Unit is equivalent to the Grouse 

 Ridge Formation of Davis and Lipman (1962) 

 

Salmon Hornblende Schist (Devonian)––Hornblende schist and gneiss, probably derived from mafic volcanic 

 rocks. Composition similar to mid-ocean ridge basalt (Barrow and Metcalf, 2006). Locally includes minor 

 lenses of micaceous schist 

 Broken formation (Lower Jurassic to Permian)—Mafic volcanic rocks, thin-bedded chert, phyllite, and mildly 

 recrystallized limestone (ls, where divided). Volcanic rocks locally have well-developed pillow structure, 

 are vesicular, and weather to shades of red and purple. Radiolarians in chert and tuff range in age from Permian 

 to Early Jurassic (Pliensbachian) (Blome and Irwin, 1983). Much of the volcanic rock may represent the upper 

 part of the North Fork ophiolite, the lower part being ultramafic rock (Pum), gabbro (Pgb), and diabase (db) that form the 

 western border of the terrane. Although the diabase is assumed to be part of the ophiolite, the genetic relation is 

 not clear

 Dots mark small limestone bodies 

 

DESCRIPTION OF MAP UNITS

UNCONSOLIDATED DEPOSITS

Eastern Klamath Terrane

Central Metamorphic Terrane

North Fork Terrane

Eastern Hayfork Terrane

Old alluvium (Quaternary and older?)—Includes old soil, colluvium, and gravel. Associated with topographically 

 high remnants of old land surfaces

Broken formation and mélange (Triassic and Permian)—Interlayered mafic volcanic rocks, slaty argillite, 

 thin-bedded chert, phyllite, quartz-keratophyre tuff and associated small intrusive bodies, siliceous sandstone, 

 grit, and pebble conglomerate. Includes minor amounts of chlorite schist, blocks of epidote amphibolite 

 (a, where divided), micaceous metachert, mica schist, recrystallized limestone (ls, where divided), and 

 serpentinized ultramafic rock (um, where divided). In addition, some patches of ultramafic rock (um) present 

 in unit Jmsv may be structural outliers. Fossils in the limestone are variously Permian and Triassic in age and, 

 at several localities, the microfauna and corals are of Tethyan faunal affinity (Irwin and Blome, 2004). Chert 

 yielded radiolarians of Permian and Triassic ages but none clearly of Jurassic age

 Dots mark small limestone bodies

 Ironside Mountain batholith and related plutons (Jurassic)—Mostly syenodiorite and pyroxene diorite; 

 locally includes quartz diorite, minor amounts of gabbro, pyroxenite (px, where divided), and contact-

 metamorphosed rocks. Part of, and restricted to, Western Hayfork terrane. Isotopic analysis (K-Ar) indicates 

 an approximate 165 Ma (Middle Jurassic) age of emplacement of the Ironside Mountain batholith (Lanphere 

 and others, 1968, p. 1038); U/Pb analysis of zircons from the Ironside Mountain batholith and related plutons 

 yielded ages of 170-163 Ma (Wright, 1981)

Rattlesnake Creek Terrane

Mélange (Jurassic to Permian)—Mainly volcanic and volcaniclastic rocks, thin-bedded chert, phyllite, and 

 serpentinized ultramafic rock (um, where divided). Volcanic rocks are commonly pillow lava, are vesicular, 

 and weather to shades of red and purple. Much chert is red and locally stained by dark oxides of iron and 

 manganese. Beyond the limits of the quadrangle, the Rattlesnake Creek terrane also includes bodies of 

 recrystallized limestone; fossils in some limestone bodies are Permian. Radiolarians in the chert are commonly 

 Triassic and, rarely, Early Jurassic (Irwin and others, 1977; Irwin and Blome, 2004). Rocks of Rattlesnake 

 Creek terrane are generally sheared and dislocated. The lithic assemblage indicates that the terrane is a highly 

 dismembered ophiolite and mélange. Surficially, the terrane is characterized by highly unstable hillsides

Western Hayfork Terrane

Metavolcaniclastic andesite (Jurassic)—Andesite that ranges in texture from coarse agglomerate to thin-bedded 

 tuff. Locally includes interlayers of dark slaty argillite and thin-bedded chert (ch, where divided). Chert at 

 several localities beyond the quadrangle contains poorly preserved Mesozoic radiolarians (Irwin and Blome, 

 2004). Intruded by:

a

Serpentinite (Ordovician?)––Probably a small isolated slice of Trinity ophiolite at base of Oregon Mountain

 outlier (see Irwin, 2009)

WEAVERVILLE FORMATION

 Any use of trade

only and does no

This map was pr

calibration may v

same plotter, and 

and proportions 

For sale by U.S. 

Denver, CO 8022

Digital files availa

 

 REFERENCES CIT

Barnett, J.C., 1982, Palynology and paleontology of the Weaverv

 Seattle, University of Washington, M.S. thesis, 118 p.

Barrow, W.M., and Metcalf, R.V., 2006, A reevaluation of the pal

 terrane, eastern Klamath Mountains, California: New constra

 chronology, in Snoke, A.W., and Barnes, C.G., eds., Geologic

 Oregon: A volume in honor of William P. Irwin: Geological S

Blome, C.D., and Irwin, W.P., 1983, Tectonic significance of late 

 terrane, Klamath Mountains, California, in Stevens, C.H., ed.

 terranes: Society of Economic Paleontologists and Mineralog

Cashman, S.M., and Cashman, K.V., 2006, Cataclastic textures in 

 in Snoke, A.W., and Barnes, C.G., eds., Geological studies in 

 Oregon: A volume in honor of William P. Irwin: Geological S

Davis, G.A., and Lipman, P.W., 1962, Revised structural sequenc

 Klamath Mountains, California: Geological Society of Amer

Irwin, W.P., 1974, Reconnaissance geologic map of the Hayfork q

 U.S. Geological Survey Miscellaneous Field Studies Map MF

Irwin, W.P., 2009, Geologic map of the Weaverville 15’ quadrang

 Scientific Investigations Map 3095, scale 1:50,000 (http://pub

Irwin, W.P., and Blome, C.D., 2004, Map showing fossil localitie

 Rattlesnake Creek terranes of the Klamath Mountains, Califor

 Report 2004-1094, scale 1:500,000, pamphlet 45 p. (http://pu

Irwin, W.P., Jones, D.L., and Pessagno, E.A., Jr., Significance of 

 of the southern Klamath Mountains, California: Geology, v. 5

Lanphere, M.A., Irwin, W.P., and Hotz, P.E., 1968, Isotopic age o

 morphic events in the Klamath Mountains, California: Geolo

MacGinitie, H.D., 1937, The flora of the Weaverville beds of Trin

 America: Washington, D.C., Carnegie Institute, Contributions 

Wright, J.E., 1981, Geology and U-Pb geochronology of the west

 Mountains, northern California: University of California, San

half of the quadrangle.

 

The small area of Eastern Klamath terrane is part of the Oregon M

the Weaverville 15' quadrangle (Irwin, 2009). It was originally m

thought by some to be part of an outlier of Yreka terrane that has 

(Cashman and Cashman, 2006). The Central Metamorphic terran

formed by the eastward subduction of oceanic crustal basalt (the 

sediments with interbedded limestone (the Abrams Mica Schist) b

Abrams Mica Schist indicates a Middle Devonian metamorphic a

which probably represents the age of subduction.

The North Fork terrane, which is faulted against the western boun

Permian(?) North Fork ophiolite and overlying broken formation 

marine metasedimentary and metavolcanic rocks. The ophiolite, w

thrust westward over the Eastern Hayfork terrane.

The Eastern Hayfork terrane is a broken formation and mélange o

of amphibolite, limestone, and serpentinized ultramafic rocks. Th

none of clearly Jurassic age. In contrast, the cherts of the North F

addition to those of Permian and Triassic ages; also, some limest

Tethyan affinity, but those of the North Fork terrane do not.

The Western Hayfork terrane is an andesitic volcanic arc that was 

metavolcaniclastic andesitic agglomerate and tuff, as well as argi

batholith, which intruded during Middle Jurassic time. Two large 

of the Eastern Hayfork terrane may be exposed through windows 

relation is not clear.

The Rattlesnake Creek terrane is a mélange that occupies only a s

however, it is a major unit in the Hyampom 15' quadrangle to the 

rocks of probable Permian or early Mesozoic age.

 

The Cretaceous Great Valley sequence overlap assemblage here p

emplacement of the Shasta Bally batholith, which is widely expo

Valley sequence once covered much of the southern Klamath Mo

patches remain near its southern boundary.

 

Weakly consolidated nonmarine sedimentary rocks of the Weaver

fossil plants, occupy a large, shallow, east-northeast-trending grab

formation overlaps the main boundary between the Eastern and W

Mineral production from the Hayfork quadrangle has been small. 

Weaverville Formation. Gold has been mined from several lode d

Hayfork terranes near their common boundary southeast of the to

quadrangle has come, however, from the mining of stream and te

the quadrangle, and along Hayfork Creek in the southern part of t

This map of the Hayfork 15' quadrangle is a digital rendition of U

MF-576 (Irwin, 1974), with various improvements and additions