BULLETIN OF THE AMERICAN ASSOCIATION OF PETROLEUM GEOLOGISTS VOL. 40. NO. 8 (AUGUST, 1956). PP. 1968-1984. 4 FIGS.

UPPER CRETACEOUS ROCKS OE PARTS OF SOUTHWESTERN OREGON AND NORTHERN CALIFORNIAi DAFJ.AS L. PECK,2 RALPH W. IMLAY,^ .^ND W. P. POPENOE^ Washington, D. C, and I>os Angeles, California

ABSTRACT The Upper Cretaceous rocks in Siskiyou County, California, and in adjoining Jackson County, Oregon, are herein defined as the Hornbrook formation. A new name to diiferentiate them from the Chico formation in California is justified by their remote position and by their nearly complete lack of faunas in common with the Chico at its type section. The Hornbrook formation comprises at least 2,500 feet of arkosic wacke sandstone, siltstone, mudstone, and conglomerate; contains fossils of Cenomanian, Turonian, and Campanian age; and includes one unconformity-

INTRODUCTION Upper Cretaceous sedimentary rocks trending northwesterly across Siskiyou County, California, and Jackson County, Oregon, have generally been referred to as the Chico group although they are more than 80 miles north of the nearest exposures of Upper Cretaceous rocks in the Sacramento Valley near Redding, Cal­ ifornia, and more than 140 miles north of the type locality of the Chico group along Chico Creek. Recently, however, F. G. Wells concluded, after field and office investigations, that the Upper Cretaceous rocks near the Oregon-California border are too far from outcrops at the Chico type locality in the Sacramento Val­ ley for the name Chico to be applicable to them (W^ells, F. G., oral communica­ tion). He felt that establishment of a new formational name for the Upper Cretaceous rocks in Jackson and Siskiyou counties would serve local mapping needs better than the term Chico group and would avoid stratigraphic misappli­ cations and misunderstandings. He decided that the proposed formation should be based on the excellent exposures near Hornbrook, California. Accordingly, to fulfill these needs, Ralph Imlay examined pertinent Creta­ ceous fossils in the collections at the National Museum and at the California Academy of Sciences. Subsequently he joined Dallas Peck for 7 days of field work in Siskiyou County, California, and 4 days of field work in adjoining parts of Oregon. Emphasis in the field was placed on determining the stratigraphic se­ quence, on obtaining critical dating fossils, and on selecting a section that would be suitable as the type of a new formation. The section selected was described and sampled, and the thicknesses of its component parts were measured by means of a clinometer. It was then remeasured with a plane table, alidade, and stadia rod. The section was selected because it is the best exposed and the most accessible in ^ Publication authorized by the director of the United States Geological Survey. ^ Geologist, United States Geological Survey, Washington, D. C, ' Geologist, University of California at Los Angeles. The writers are indebted to F. G. Wells for many suggestions during the preparation of this re­ port. Professor Howel Williams supplied a field map of the Hornbrook area and information on a plant locality in volcanic rocks of Tertiary age. Local residents, C. B. Kay of Montague, California, W. B. Pollock of Yreka, California, and Chester Fitch of Medford, Oregon, generously supplied many fossil specimens and contributed their time and knowledge in the search for more fossils.

1968 UPPER CRETACEOUS, OREGON AND CALIFORNIA 1969 the Hornbrook area. Probably not more than 10 per cent of the rocks are covered along the course measured. W. P. Popenoe did not work with Peck and Imlay in the field, but he has studied the Cretaceous rocks along the Oregon-California boundary and has contributed considerable unpublished stratigraphic and paleontologic data that are included herein. M ost of the correlations with sections in the Sacramento Valley and in southern California are based on his fossil determinations and his field investigations. In the following text, Imlay and Popenoe are responsible for all statements concerning fossils and correlation. Peck is reponsible for the remainder of the report.

HISTORICAL SUMMARY Gabb (1869) established the name Chico group for the strata between what was then identified as the Martinez and the Shasta groups in the Pacific Coast area from Vancouver Island to southern California. He established the typical localities at Chico Creek, Pence's Ranch, and Tuscan Springs on the east side of the Sacramento Valley, California, and noted that the Chico group "includes all the known Cretaceous of Oregon and of the extreme northern portion of Cali­ fornia." Diller (1893) briefly described the occurrence of rocks of Chico age near Yreka, California, and on Grave Creek, Oregon (Fig. i). Dunn (1894) and Turner (1903) described in detail the lithologic character and thickness of the auriferous conglomerate at the base of the Upper Cretaceous rocks in Cottonwood Creek Valley, Siskiyou County, California. Anderson (1902) supplied fossil lists and described the gross stratigraphic features of the Upper Cretaceous rocks in Cot­ tonwood Creek Valley and in the Bear Creek Valley, Jackson County, Oregon. In 1931, Anderson described the section of Upper Cretaceous rocks near Hornbrook as follows. Their lower part consists of sandy strata having a total thickness of about 2,000 feet. At the base they contain conglomerates; higher up, but below the middle of the sandy beds there are thin bedded sandstones well filled with marine fossils, including many species of bivalves and gastropods; at the top the sandstones are overlaid by clay shales nearly 1,000 feet in thickness, forming here the upper one third of the Cretaceous sequence. At the junction of the uppermost sandstone l)etls and the overlying shales is the second notable zone of fossils, Avhich contains few of those found in the lower zone, but instead a considerable variet}' of cephalopod forms. Anderson suggested that the lower zone is about middle Turonian and that the upper zone is upper Turonian and lower Senonian. Later, Anderson (1943) published a paper in which he raised the Chico of the Pacific Coast to series rank, and divided it into three groups and nine stages. Unfortunately, his subdivisions are not tied to a type section and are very briefly described, and the name of the lowest group, Pioneer, is pre-empted. Diller and Kay (1924) briefly described the lithologic character and thickness of the Upper Cretaceous strata on Grave Creek, and Wells (1939) described the lithologic character and thickness of the Upper Cretaceous rocks in the Aledford 1970 DALLAS L. PECK, ET AL.

_Jt»»00'

EXPLANATION

^^ Upper CrCtOCtOUB Rocks

FIG. I.—Index map of part of southwestern Oregon and northern California, showing areal dis­ tribution of Upper Cretaceous rocks. Data from Diller and Kay (1924), Wells (1939), and modified from Williams (1949). UPPER CRETACEOUS, OREGON AND CALIFORNIA 1971

Quadrangle, Oregon. Recently Williams (1949) described the location and litho- logic character of the Upper Cretaceous rocks in the Yreka Quadrangle, Cal­ ifornia.

STRATIGRAPHY AND LITHOLOGY

GENERAL DESCRIPTION OF HORNBROOK FORMATION Discontinuous exposures of well consolidated, well bedded, clastic sedimen­ tary rocks of Late Cretaceous age form a northwest-trending band that extends from near Yreka, California, along the valleys of Cottonwood and Bear Creeks to Grave Creek, Oregon (Fig. i). The Upper Cretaceous rocks non-conformably overlie deformed and in part metamorphosed volcanic and sedimentary rocks ranging in age from Paleozoic to Late Jurassic and granitic intrusive rocks of Late Jurassic or Early Cretaceous age. In turn, the Upper Cretaceous rocks are overlain disconformably by clastic sedimentary rocks and volcanic rocks of Eocene age. The writers propose that these Upper Cretaceous sedimentary rocks in south­ western Oregon and northernmost California be named the Hornbrook formation, and that the type section be designated as the exposures near the town of Horn- brook, California, as shown graphically in Figure 3 and as described and located in detail herein. In the vicinity of Hornbrook the beds of Upper Cretaceous age occupy the center and the western slope of the valley of Cottonwood Creek (Fig. 2). The beds strike N.NW. and dip is°-2S° NE. They unconformably overlie steeply dip­ ping argillite and mafic volcanic flows and mudflows of the Applegate group of Triassic age which have been metamorphosed to epidote-albite amphibolites. F. G. Wells (oral communication) traced the argillite and volcanic rocks into fossiliferous Triassic Applegate in the Grants Pass Quadrangle, Oregon. Overlying the Upper Cretaceous strata are non-marine silty shales and sandstones of Eocene age which are in turn overlain by lava flows, mudflows, and tuffs of Eocene age. The Cretaceous-Eocene contact was not found in the Hornbrook area, but Wells (1939) reports that in the near-by Medford Quadrangle, Oregon, the Eocene sedi­ ments "apparently rest disconformably upon Chico." The complete thickness of the Hornbrook formation near Hornbrook has not been determined. A thickness of 2,673 + 50 feet was measured, but of this the upper 615 feet of mudstone did not furnish megafossils and was not sampled for microfossils. Stratigraphically above the measured section is about 1,000 feet of poorly exposed, similar appearing mudstone that may also be late Cretaceous and which in turn is overlain by about 1,000 feet of mudstone that contains thin beds of micaceous and tuffaceous sandstone. These mudstone beds are lithologically similar to non-marine fossiliferous sediments of upper Eocene age in the Medford Quadrangle, Oregon, described by Wells (1939), and may be of the same age. The basal tuff of the overlying volcanics in the Hornbrook area has yielded fossil leaves identified by C. Condit (written communication to Howel Williams) 1972 DALLAS L. PECK, ET AL.

EXPLANATION

Mamber 6, Hornbrook formotion

Members 5,4 ond 3, Hornbrook formotion

Members 2 and I, Hornbrook formation ,25 T Strike and dip of beds * ^Line of measured sections Approximate contact Inferred contact ^5£?o > Structure Contour *H°

Bas« modified from Geology by US as. 1947 Imloy ond Peck, 1954

FIG. 2.- Skelch map of geology in Hornbrook area, California, showing location of measured section. which R. W. Brown (oral communication) has called Eocene. Determination of the total thickness of the Upper Cretaceous strata in the Hornbrook area will probably require microfaunal studies in conjunction with detailed mapping. The Hornbrook formation grades generally upwards from conglomeratic sand­ stone through interbedded sandstone and siltstone to mudstone. The section near Hornbrook consists of three stratigraphic divisions, each of which grades upward from coarser- to finer-grained (see Figure 3). The contact between the lower two divisions (members II and III) appears to represent an erosional break, which on the basis of fossil evidence seems to represent Coniacian and Santonian time. In the Hornbrook area the sandstone and coarse siltstone are well consolidated and well bedded, mostly ranging from thin- to thick-bedded. The sandstone is coarse- to very fine-grained and contains poorly sorted subangular to subrounded grains of quartz, feldspar, and lithic fragments in a subordinate finer-grained chloritic matrix. The fine-grained sandstone and coarse-grained siltstone contain conspicuous fresh biotite that imparts an indistinct lamination to the rocks. The coarse- and medium-grained sandstone contains scattered pebbles and angular shale fragments. Cross-bedding is rare. Graded bedding was not observed. Very fresh sandstone is grayish green to greenish gray; slightly weathered sandstone is olive-gray to light olive-gray; and weathered sandstone is olive-gray to yellowish gray or dusky yellow. Lichen mottling imparts a dark cast to some outcrops. MEMBER FEET SECTION INCOMPLETE DIAGNOSTIC FOSSILS

Mudstooe, olive gray, hard; some calcareous concretions (in lower half only) throughout and thin beds of olive gray, fine grained lithic Metaplacentictras pacificum (Smith) wacke sandstone near top. litocertnms sp.

}AetaplacenticeTas pacijicum (Smith) Metaplactnticeras califomicum (Anderson) Desmopbylliles? sp. Siltstone, thin bedded, olive gray, coarse grained; alternat­ Lytoctras (GaadTyctras), ci.G. ^rfenwiwenje (Whitcaves) ing with some pale olive, fine grained arlcosic wacke P achydiscus sp. sandstone. Eupacbydiscus ci.E. perpticatus (Vhiieaves)' Eupachydiacus ci.E. haradai (Jimbo) tnoctramus cf. I. pertenuis Meek and Hayden

Sandstone, medium to thick bedded, light olive gray, very No fossil evidence fine grained arkosic wacke.

Siltstone, oonbedded to faintly laminated, light olive gray, fine grained, hard. No fossil evidence

^^ Sandstone, alternating thin and medium bedded, olive gray, No fossil evidence ^'Ka very fine grained.

Sandstone, massive, greenish gray, medium grained, arkosic No fossil evidence wacke; contains basal conglomerate.

Sandstone, thin bedded, dark gray, very fine grained; con­ No fossil evidence tains calcareous concretions near top

Sandstone, alternating thick and thin bedded, grayish green, Collignoniceras? Sp. very fine grained arkosic wacke; contains basal con­ inoceramus klamatbtnsis Anderson Trigonia cf. T. tvansana Meek glomerate. Calva ct. C. regina Popenoe

Subprionocyclus Sp. Sandstone, chin to medium bedded, pale olive, very fine to Calva cf. C. regina Popenoe medium grained, arkosic wacke; contains a thick bed of Tngonia cf. T. evansam Meek massive, pebbly sandstone in lower third and a bed of Cucullata cf. C. gravida (Gabb) noobedded soft brown sandy siltstone at base. Turriteila cf. T. iota Popenoe InoctTamus klamathensis Anderson

Angular Unconformity .

Total 2673 Metavolcanic mafic flows and agglomerates of the Triassic Applegate group.

FIG. 3.—Columnar section of Hombrook formation near Hornbrook, California. 1974 DALLAS L. PECK, ET AL.

The average composition of five thin sections from sandstones of members I, II, III, and V is as follows: feldspar 33%, quartz 24%, matrix 21%, rock frag­ ments 14%, biotite 5%, epidote 1%, and magnetite and calcite 2%, plus traces of sphene, zircon, green hornblende, olivine, and hypersthene. Following Gilbert (1954), the sandstones are classified as arkosic wacke (matrix >io%, feldspar > 25% and feldspar more abundant than lithic fragments). The feldspar is mostly oligoclase, but it ranges from albite to andesine and includes very minor potash feldspar. A few of the quartz grains are recrystallized. The rock fragments are mostly of mafic metavolcanic rocks, but a few are fine-grained quartzose rock (quartz schist and sillstone). The biotite is partly altered to chlorite. The matrix is composed of chlorite and fine detrital grains of quartz and feldspar. Throughout the sandstones chlorite has partly replaced the lithic fragments and to a lesser extent the feldspar grains. Of somewhat different composition is the fine-grained sandstone at the top of the measured section. A thin section contains 32% lithic fragments, 23% feld­ spar, 20% matrix, 18% quartz, 6% biotite, and 1% magnetite and epidote. The sandstone is classified as a lithic wacke (i.e., matrix > 10%, lithic fragments > 10% and lithic fragments more abundant than feldspar). The coarse-grained siltstone is similar in composition to the sandstone but contains relatively more matrix and fewer lithic fragments. A thin section of a coarse-grained siltstone of member V contains 51% matrix, 22% quartz, 14% feldspar, 7% biotite, and 6% lithic fragments, magnetite, epidote, and sericite. The fine-grained siltstone and mudstone in the Hornbrook formation are non- bedded to indistinctly laminated, hard, and typically break into small irregular to spindly fragments. The rocks contain 10-50% silt-size grains of quartz and feldspar in a chloritic and micaceous matrix. The mudstone and siltstone are olive gray to light olive-gray and weather yellowish gray. The basal beds of the Hornbrook formation are not highly conglomeratic along the Klamath River. On the north side of Rocky Gulch in the SE. \ of Sec. 30, T. 47 N., R. 6 W. (Fig. 2), the basal conglomerate is 87 feet thick and forms massive gray cliffs separated by steep rubble covered slopes. The pebbles and cobbles are as much as 6 inches in diameter, well rounded but poorly sorted, and are set in a matrix of small well rounded to subrounded pebbles, granules, and coarse sand. The particles of gravel size are composed of mafic volcanics, quartz- ite, argillite, and some felsite. The matrix is composed of about equal amounts of quartz, feldspar, and lithic fragments in a calcite cement. The exact contact with the underlying metavolcanics is concealed in Rocky Gulch but is exposed in Rancheria Gulch, a few miles north. Dunn (1894) and Turner (1903), who de­ scribed the conglomerate when it was being mined for placer gold, report that the conglomerate is about 170 feet thick at Rancheria Gulch and Ditch Creek but is replaced by sandstone north of Ditch Creek and on the ridges between Ditch Creek, Rancheria Gulch, Rocky Gulch, and the Klamath River. This suggests an onlapping relationship between the sandstone and conglomerate. The lithologic UPPER CRETACEOUS, OREGON AND CALIFORNIA 1975

composition of the conglomerate also differs laterally, apparently as a result of lithologic variation of the underlying pre-Cretaceous rocks. According to Turner (1903) and Dunn (1894), the conglomerate in Rancheria Creek and at the Blue Gravel Mine, | mile northwest of the Klamath River, contains less metavolcanic rock and more quartz, quartzite, and granite rock than in Rocky Gulch. Williams (1949) reports that northeast of Yreka the conglomerate is made up of milky quartz, quartzite, and black chert plus porphyry and quartz diorite. The Upper Cretaceous rocks in the Medford Quadrangle resemble lithologi- cally the lower third of the formation near Hornbrook. As described by Wells (1939) the rocks are "fairly uniform in texture and composition and consist of a hard, fine grained, greenish-gray, arkosic sandstone with local lenses of coarse con­ glomerate and sandy shales." The conglomerate "consists of ill-sorted but well- rounded pebbles and a few cobbles, which are composed mainly of metamorphic rocks, although they include granitic rocks and white vein quartz as well as argil- lites, and metavolcanics." The maximum thickness of the Upper Cretaceous rocks is 600 feet. Farther north, on Grave Creek, the Upper Cretaceous rocks, as described by Diller and Kay (1924) are "chiefly sandstone, with considerable conglomerate at the base and some shale." The thickness is 50-200 feet.

DETAILED DESCRIPTION OF HORNBROOK FORMATION In the Hornbrook area the Hornbrook formation consists of six unnamed mem­ bers, which have been traced northward from the south side of the Klamath River to the vicinity of Hilts. The members are numbered I to VI from oldest to youngest. Along the Klamath River, member I is 446 feet thick and consists predomi­ nantly of thin- to medium-bedded, moderately resistant, medium- to very fine­ grained, pale olive sandstone. About 120 feet above its base are 40 feet of more resistant, slightly cross-bedded, massive pebbly sandstone that is capped by 8 feet of poorly sorted conglomerate. The conglomerate contains well rounded pebbles and cobbles, mostly of mafic volcanic rock and lesser granite, quartzite, and argillite. The conglomerate includes many thick-shelled oysters, clams, and gastropods. The basal 31 feet of the member is soft, poorly sorted, non-bedded, pale brown siltstone. In sharp contact with member I is member II, which consists of 266 feet of sandstone. The basal 24 feet of sandstone is thick-bedded, ledge-forming, medium- grained, grayish green, and contains lenses of pebbly sandstone and abundant shells of bivalves and gastropods. The overlying 112 feet of sandstone is moder­ ately resistant, very fine-grained, grayish green, and comprises alternating thick and very thin beds. Some molds of bivalves, gastropods, and ammonites occur near the top. The upper 130 feet of sandstone is non-resistant, very fine-grained, dark gray, mostly irregularly thin-bedded but includes subordinate amounts of more resistant medium-bedded sandstone. Small carbonized plant fragments are 1976 DALLAS L. PECK, ET AL. abundant along bedding planes. The sandstone is generally poorly exposed, but its stratigraphic position is indicated by grass-covered slopes beneath the cliff-form­ ing sandstone of member III. In the upper lo feet are many calcareous concretions 2-8 inches in diameter that become increasingly abundant upward. The overlying member III consists of 134 feet of massive, cliff-forming, medium-grained, greenish gray sandstone. Scattered through it are pebbles and angular shale fragments, and in its basal few feet are numerous pebbles and cal­ careous concretions. The concretions are identical with those in the upper part of the underlying sandstone and apparently were derived from it. Member III con­ tains a few thin silty shale lenses with which are associated large pebbles and cobbles of quartz, felsite, and granitic rock. The contact with the underlying member is sharp but appears indistinct in detail, apparently because of the presence in the basal few feet of member III of material derived from the under­ lying sandstone. Member IV is 372 feet thick in the area between the Klamath River and Rancheria Gulch. The lower 70 feet consists of moderately resistant, olive-gray, thin beds of fissile sandy siltstone and fine- to coarse-grained sandstone. The upper 302 feet consists mostly of light olive-gray fine-grained shaly siltstone but includes a few thin beds of coarse-grained sandstone in its lower half. The overlying member V is 311 feet thick where measured near Rancheria Gulch. Its lower 181 feet consists of medium- to thick-bedded, resistant, very fine-grained, light olive-gray sandstone. The upper 130 feet of the member con­ sists of moderately resistant, coarse-grained, ohve-gray siltstone that includes a few thin beds of resistant, coarse-grained, light olive-gray sandstone. The sand­ stone beds contain common calcareous concretions as much as several feet in diam­ eter. On the low hills west of Henley and on the slopes south of the Klamath River, some of these concretions have yielded ammonites. Member VI is 1,128 feet thick in the area between Rancheria Gulch and Ditch Creek. It consists almost entirely of non-bedded, hard, olive-gray mudstone that forms low, rounded slopes and weathers into irregular or spindly pieces. It includes many dark greenish gray, pyritic, calcareous concretions, some of which bear frag­ ments of Inoceramus. Near the top of the measured section are thin beds of ledge- forming, fine-grained, olive-gray, lithic wacke sandstone.

MEASURED SECTION OP HORNBROOK TORMATION The following section of the Hornbrook formation is composite. Members I, II, III, and the lower 70 feet of IV were measured along the west side of U. S. Highway 99 from the basal contact in the NE. j, SE. J of Sec. 32 to the SE. j, SE. I of Sec. 29, T. 47 N., R. 6 W. (Fig. 2). The rest of member IV and all of member V were measured along the ridge south of Rancberia Gulch from the NW. i, NW. J of Sec. 29 to near the middle of the SW. J of Sec. 20, T. 47 N., R. 6 W. Member VI was measured between Rancheria Gulch and Ditch Creek from the SW. i of Sec. 20 to the SE. |, SW. i of Sec. 17, T. 47 N., R. 6 W. UPPER CRETACEOUS, OREGON AND CALIFORNIA 1977

Umpqua formation (not studied) Hornbrook formation (top not determined) Member VI (incomplete) Feei Unit 18. Sandstone, medium-bedded, fine-grained, olive-gray; weathers dusky yellow 5 Unit 17. Mudstone, hard, olive-gray; weathers yellowish gray; forms low rounded slopes 68 Unit 16. Sandstone, ledge former, fine-grained (1-4-foot) beds separated by mudstone partings, olive-gray; weathers dusky yellow 20 Unit 15. Mudstone, non-bedded, ohve-gray; weathers yellowish gray, breaks into small irregular or spindly pieces, contains many dark greenish gray, pyritic, calcareous con­ cretions 1-4 inches in diameter that weather yellowish brown and may contain frag­ ments of Inoceranms shells; Metaplacenticeras obtained from lower part; forms low, rounded slopes i > 03S

Total thickness of member VI i, 128 Member V Unit 14. Siltstone, thin-bedded, coarse-grained, medium olive-gray to light olive-gray; weathers yellowish gray; contains a few thin beds of more resistant, very fine-grained, pale-olive sandstone, which contains common calcareous concretions as much as sev­ eral feet in diameter; concretions have yielded Metaplacenticeras and pachydiscid am­ monites; forms rounded slopes 130 Unit 13. Sandstone, medium- to thick-bedded, very fine-grained, light olive-gray; weathers darker gray; conspicuous biotite flakes impart indistinct lamination in some beds; grades into overlying siltstone unit; forms low hills 181

Total thickness of member V 311 Member IV Unit 12. Siltstone, massive to indistinctly laminated, hard, shaly, fine-grained, light olive-gray; weathers same color or has reddish brown stain, breaks into small irregular pieces; occurs partly as 2-6-inch beds interbedded with 1-4-inch beds of slightly more resistant, coarse-grained siltstone; lower half of unit has several fairly resistant, 8-12- inch thick lenses of coarse-grained, gray sandstone and olive-gray, calcareous siltstone that weathers reddish brown; unit forms low, rounded slopes 302 Unit II. Sandstone, thin-bedded; very fine-grained sandstone and siltstone interbed­ ded with medium-bedded, fine- to coarse-grained sandstone, olive-gray; weathers yel­ lowish gray; forms low hills 70

Total thickness of member IV 372 Member III Unit 10. Sandstone, cliff-forming, massive, medium-grained, very well consolidated, greenish gray; weathers yellowish gray and is locally cavernous; contains small, round­ ed pebbles of metamorphic rock and angular shale fragments scattered throughout; the unit has several thin lenses of silty shale that may include large rounded pebbles and cobbles of quartzite, vein quartz, felsite, and granite; basal few feet has concen­ tration of pebbles and calcareous concretions, the latter apparently derived from un­ derlying unit; basal contact sharp

Total thickness of member III 134 Member II Unit Q. Sandstone, mostlj' irregularly thin-bedded, very fine-grained, dark gray; weath­ ers olive to yellowish gray; some more resistant beds 1-2 feet thick that weather to rounded slabs; abundant small carbonized plant fragments present along bedding planes; dark gray, calcareous concretions 2-8 inches in diameter occur in upper 10 feet and become increasingly abundant upward; forms rounded saddles 130 Unit 8. Sandstone, alternating thin- and thick-bedded, strata as much as 10 feet thick, very fine-grained, grayish green; weathers yellowish gray; biotite prominent, especially in the thin beds; some external molds of bivalves, ammonites, and gastropods present; ColUgnoniceras and Inoceramus klamathensis Anderson found near top 132 Unit 7. Sandstone, massive to thick-bedded, mostly fine-grained, grayish green; weathers yellowish gray; biotite prominent; pebbly at the base and in lenses through­ out; pebbles are small, rounded, poorly sorted, dark greenish gray, consist of meta­ morphic and igneous rock, and occur in a matrix of coarse sand and granules; shells of bivalves and gastropods are common in pebbly beds; unit forms ledges 24

Total thickness of member II 286 1978 DALLAS L. PECK, ET AL.

Feet Member I Unit 6. Sandstone, thin to medium-bedded, very fine-grained, pale olive; weatliers yel­ lowish gray; conspicuous biotite imparts faint lamination; moderately resistant, form­ ing hills 2/5 Unit 5. Conglomerate, massive, poorly sorted, well rounded granules, pebbles, and cob­ bles of mafic metavolcanics, less amounts of granite, quartzite, and argillite, and minor amounts of gabbro, vein quartz, and rhyoUte in matrix of subrounded, fine to coarse sand; weathers yellowish gray; thick-shelled oysters, clams, and gastropods are fairly common 8 Unit 4. Sandstone, pebbly, upper 40 feet thick-bedded to massive, sUghtly cross-bedded, cliff-former; overlies less resistant, alternating thin and medium beds; sand grains very fine to coarse, poorly sorted; pebbles subrounded, scattered and in lenses, composed mostly of quartzite, granite, and mafic metavolcanics; biotite conspicuous in fine­ grained sandstones; some angular shale fragments present; many thick-shelled bivalves and gastropods associated with pebbly beds; lower 80 feet poorly exposed 120 Unit 3. Sandstone, thick-bedded, medium- to coarse-grained; weathers dusky yellow; ledge-forming 7 Unit 2. Sandstone, very poorly consolidated, very poorly sorted; contains angular peb­ bles of mafic metavolcanics and granitic rock in matrix of clay, silt, and sand-size ma­ terial ; weathers pale brown i Unit I. Siltstone, sandy, poorly sorted, soft, non-bedded; contains minor amounts of granules and pebbles consisting of mafic metavolcanic rock; forms rounded saddles; basal few feet concealed 31

Total thickness of member I 442

Total measured thickness of Hornbrook formation 2,673±50 Applegate group (not studied)

COKRELATION The Hornbrook formation in Siskiyou County, California, contains ammonites of middle to late Turonian age in the upper part of member I and in the lower part of member 11. It contains ammonites of Campanian age in the upper part of member V and in the lower part of member VI. It has not furnished fossils repre­ senting Coniacian and Santonian ages. These ages and probably part of the Cam­ panian age may be represented by the 800 feet of barren rock between the lower part of member II and the upper part of member V, or may be represented by an unconformity between members II and III. The Hornbrook formation in Jackson County, Oregon, is similar in thickness and lithologic features to, and is identical faunally with, members I and II of the type section in Siskiyou County, California. It does not contain the lithologic sub­ divisions represented by members III-VI of the type section. Rather extensive fossil collecting in Jackson County by field parties of the U. S. Geological Survey has furnished fossils only of Cenomanian and Turonian age. IMany fossils of younger age are listed by Anderson (1902, pp. 27-32) as occurring near Phoenix in Jackson County, but he correlates (1902, pp. 39, 40) the Cretaceous strata in that county with the so called "Lower Chico" in California, and the only species from Oregon that he illustrates are of Cenomanian and Turonian ages. If the ammonite Melaplacenticeras is present near Phoenix, as stated by Anderson (1902, pp. 79, 80), the Hornbrook formation must thin markedly northward from the Horn­ brook area. That is a possibility that should be investigated because a similar thinning of the sandstone units in the formation occurs southward from Horn- UPPER CRETACEOUS, OREGON AND CALIFORNIA 1979 brook in the area south of Black Mountain. Near Henley the lowest beds contain­ ing Melaplacenticeras and Eupachydiscus occur about 800 feet above beds con­ taining Turonian fossils. South of Black Mountain in Sec. 26, T. 46 N., R. 6 W., the beds containing Eupachydiscus occur only 200-300 feet above Turonian beds. The Turonian beds are also much thinner here than they are near Henley. The Cenomanian age of the basal Cretaceous strata in Jackson County is proved by the presence of a well preserved specimen of the ammonite Manlelli- ceras from a sandstone quarry about one mile northwest of the center of Jackson­ ville in the SW. j- of Sec. 29, T. 37 S., R. 2 W. Another bit of evidence is a large fragment of an ammonite from Dark Hollow in Sec. 13, T. 38 S., R. 2 W. This am­ monite has the peculiar ribbing characteristic of Anagaudryceras sacya (Forbes), which ranges from the late Albian into the Cenomanian in Japan and India and occurs in the middle to late Albian in Alaska. Another ammonite that might be of Cenomanian age was obtained on Grave Creek, 10 miles above Placer. It is an acanthoceratid similar to Ammonites iurneri White (not Sowerby) from the Berke­ ley area of California. Neither of these acanthoceratids agrees in all particulars with any described genus, but their resemblance to the Cenomanian genus Acanthoceras suggests that they are of that age. All the other Upper Cretaceous collections from Jackson County, Oregon, and all the collections from members I and II of the Hornbrook formation in Siskiyou County, California, contain moUusks of Turonian age. The assemblage is large, only partly described, and includes species and genera characteristic of the Glycymeris pacificus fauna (Popenoe, 1942, pp. 178-83). These include the pelecypods Glycymeris pacificus (Anderson), Caha cf. C. regina Popenoe, Trigonia evansana Meek, Trigonia leana Gabb, Cymbophora gabbiana (Anderson), Pachy- cardium? remondianum (Gabb), Inoceramus klamathensis Anderson; the gastro­ pods Gyrodes dowelli White, Pugnellus manubriatus (Gabb), Turritella cf. T. iota Popenoe; and the ammonites Collignoniceras bakeri (Anderson), C. branneri (Anderson), Prionocyclus crenulata (Anderson), Subprionocyclus knighleni (An­ derson), S. siskiyouensis (Anderson), 5. muUicosta (Anderson), Tragodesmoceras ashlandicum (Anderson), and several species of the small scaphitid Otoscaphites (equals Yezoiles). Among these ammonites, Collignoniceras (equals Prioniropis) is good evidence of a middle Turonian age and Prionocyclus of a late Turonian age. Subprionocyclus (equals Oregoniceras of Anderson) is known from the late Turonian of western Europe and Japan (Wright and Matsumoto, 1954, p. 130). Tragodesmoceras is widespread in the Turonian, but one species has been reported from the Coniacian. Otoscaphites is known elsewhere from beds of Turonian to Coniacian age (Wright, I9S3. PP- 475. 476). The relative stratigraphic position of these ammonites in the Hornbrook for­ mation is not well known. Subprionocyclus was obtained from near the middle of member I at the flume across Rancheria Gulch in the SE. J of Sec. 19, T. 47 N., R. 6 W., Siskiyou County, California. A collection of Subprionocyclus was igSo DALLAS L. PECK, ET AL. made by W. P. Popenoe probably 250 feet higher. Fragm.ents of Collignoniceras were found near the top of unit 8 of member II near U. S. Highway 99 in the NE. i of Sec. 32, T. 47 N., R. 6 W., Siskiyou County. In Jackson County, Oregon, the ammonites Tragodesmoceras and Suhpriono- cyclus were found perhaps 100 feet below the top of the formation on the Chester Fitch Ranch in the NE. |, NW. i of Sec. 18, T. 38 S., R. i W. Most of the Oregon collections described by Anderson in 1902 were from Cretaceous rock at the "49" Placer Mine on the north slope of a ridge located in Sec. 21, T. 38 S., R. i W., about 15 miles southwest of Phoenix. According to Chester Fitch, the fossils were obtained from concretions in the placer gravels that were being mined by F. M. Anderson's older brother. T. W. Stanton's notes of August 22, 1900, state, how­ ever, that the fossils at the "49" Mine occur in concretions embedded in a few feet of sandstone that overlie decomposed igneous rocks. It is possible, of course, that Anderson obtained his fossils from a gravel overlying the sandstone from which Stanton collected. Evidently the collections were made very close to the base of the Cretaceous sequence. Another large molluscan collection of Turonian age, as shown by the presence of Tragodesmoceras and Collignoniceras, was made by T. \V. Stanton on Grave Creek about 8 miles above Placer in the NE. J, SE. J of Sec. 6, T. 34 S., R. 4 W., Jackson County. According to Stanton's field notes the collection was made from 50 to 100 feet above the base of the local Cretaceous sequence, which has a total thickness of 200-300 feet. The Glycymeris pacificus fauna contains Turonian ammonites elsewhere in California, such as those in collections made by W. P. Popenoe in the Santa Ana Mountains and in the Redding area (examined by Imlay). In neither area is there faunal evidence for a Cenomanian age. Likewise, the thickness of Upper Cretace­ ous strata beneath the lowest occurrence of Turonian ammonites seems insuffi­ cient to account for the Cenomanian. In the Santa Ana Mountains Popenoe (1942, pp. 178-82) found Subprionocyclus in the Baker Canyon conglomerate member of the Ladd formation and in overlying beds transitional into the Holz shale mem­ ber. In the Redding area (Popenoe, 1943, p. 312), he found Tragodesmoceras at several levels between 300 and 550 feet above the base of member I, the Turonian Romaniceras in the basal parts of members II and IV, and Subprionocyclus in the lower parts of members II and III. Interestingly, the highest occurrence of Romaniceras in member IV is near the top of the local range of the Glycymeris pacificus fauna. An Upper Cretaceous fauna, much younger than the Turonian, is widespread in Siskiyou County, California, in the upper part of member V and the lower part of member VI of the Hornbrook formation. From unit 14 in member V on the south side of the Klamath River in the SW. |-, NE. J of Sec. 33, T. 47 N., R. 6 W., was obtained Melaplacenticeras pacificum (Smith), M. californicum {Andei- son), Desmophyllites sp. juv., Gaudryceras cf. G. denmanense (Whiteaves), Pachydiscus sp., Eupachydiscus cf. E. perplicakis (Whiteaves), E. cf. E. haradai IP PER CRETACEOUS, OREGON AND CALIFORNIA 1981

(Jimbo), a nautiloid cephalopod, Inoceramus cf. /. pertenuis Meek and Hayden, and several other i)elecypods and gastropods. From the west side of Cottonwood Valley near Henley, Anderson (1902, pp. 78, 80, 90, 98) obtained Melaplacenli- ceras pacificum, M. californicum, Pachydiscus henleyensis Anderson, Damesites sugata (Forbes), and Hamites armatum Ander. The last appears to be identical with the earlier described Didymoceras cooperi (Gabb). Large coarsely ribbed pachydiscid ammonites have also been obtained by Anderson and by local collec­ tors on the Richardson Ranch south of Black Mountain, in Sec. 26, T. 46 N., R. 6 W. These fossils are excellent evidence for a Campanian age and strongly favor middle to late rather than early Campanian. Metaplacenticeras is recorded out­ side of California only from Japan in beds that the Japanese paleontologists con­ sider to be late Campanian (Matsumoto et al., 1953, p. 15, PI. 15 opp. p. 186), but which may not be younger than middle Campanian. Didymoceras occurs in the western interior of the United States in the late Campanian (Cobban and Ree- side, 1952, PL I, p. 1020), in Vancouver Island in beds referred by Ushur (1952, p. 40) to the early Maestrichtian, and in Angola in the Maestrichtian (Spath, 1953, p. 50). It is unknown below the middle Campanian. Damesites in Japan ranges from the Coniacian to the Maestrichtian (Matsumoto et al., 1953, p. 14) and the species D. sugata (Forbes) occurs through the Santonian and Campanian. The genus occurs at many places in the Southern Hemisphere in beds of Conia­ cian to Maestrichtian age. The smooth forms similar to D. sugata are considered typical of the Campanian. The large, coarsely ribbed pachydiscids, referred to as Eupachydiscus, are of worldwide occurrence in the upper Santonian and Cam­ panian (Matsumoto, 1953, pp. 281-87) ^^^ ^^re rare in the lower ^Maestrichtian. Metaplacenticeras and coarsely ribbed Eupachydiscus identical specifically with those near Yreka occur at several places in southern California. One of these is in the Pleasants sandstone member of the Williams formation in the Santa Ana Mountains (Popenoe, 1942, p. 184), the topmost part of the Cretaceous there. In this member, also, occur Desmopkyllites, Anapachydiscus, Pachydiscus, and the uncoiled ammonite Glyptoxoceras. One specimen of Canadoceras was found in the underlying Holz shale member of the Ladd formation about 450 feet below the beds containing Metaplacenticeras. These ammonites furnish strong evidence of a Campanian age. Glyptoxoceras ranges through the Campanian and ^Maestrichtian. Anapachydiscus ranges from the Coniacian to the Maestrichtian and is most common in the lower Campanian. Desmophyllites ranges from the Coniacian to Maestrichtian, but is most common in the Campanian and Maestrichtian. Metaplacenticeras in Japan occurs a little above beds containing Submortoniceras which is a widespread characteristic early Campanian ammonite. The records of Canadoceras in Vancouver Island (Ushur, 1952, pp. 34-39) and Japan (Matsumoto, 1953, pp. 15, 290-311) show that the genus is characteristic of the Campanian, but that it probably has a longer range. Metaplacenticeras has not been found in the Redding or Chico Creek areas in 1982 DALLAS L. PECK, ET AL.

northern California. However, in the highest beds at Chico Creek, Popenoe has found certain species of pelecypods and gastropods that are associated with Metaplacenticeras in southern California. This is interesting because the under­ lying beds at Chico Creek contain the early Campanian ammonite. Suhmorton- iceras. Evidently in California as in Japan Metaplacenticeras can be assigned to the Campanian above the range of Submortoniceras. Popenoe's unpublished stud­ ies indicate that all the Cretaceous strata in the Redding area are older than the Metaplacenticeras beds. The magnitude of the unconformity between members II and III in the Horn- brook area is not known. The 700 feet of non-fossiliferous rock above the un­ conformity and the 100 feet of non-fossiliferous rock below the unconformity could represent either much or very little of the Coniacian to early Campanian stages. More detailed studies must be made of the Cretaceous strata in the Hornbrook area and in other areas in northern California before this problem can be solved. The presence of an unconformity within the Hornbrook formation may lead eventually to its division into two, or more, formations. If future mapping demonstrates that more than one formational name is necessary, the writers sug­ gest that the term Hornbrook be restricted to members I and II because such a procedure would avoid the necessity of renaming the Upper Cretaceous strata in Jackson County, Oregon. Comparisons of the time span of the Hornbrook formation with the Chico for­ mation at its type locality (Fig. 4) shows that most of the Hornbrook formation is either younger or older than the Chico formation and that the unconformity within the Hornbrook formation represents most and perhaps all of the time represented by the Chico formation. Furthermore, Figure 4 shows that the Cretaceous sequence in the Redding area, which lies between the Chico and Horn­ brook areas, is mostly older than the type Chico formation. These time relation­ ships emphasize that the history of sedimentation was considerably different in the three areas; therefore, distinct formational names are needed for each area in order to avoid ambiguity in geologic discussions. If only one formational name were used for the three areas, it would need to be qualified whenever used by the name of the area under discussion. The usage of Chico as a stratigraphic term was discussed by Popenoe and Im- lay with many geologists and the conclusion was reached that Chico should be abandoned as a group or series name because it has been used with many different meanings, but that it might usefully be retained as a formational name for the rocks at and near the type locality on Chico Creek. Thus restricted the name is applied to rocks of late Coniacian to early Campanian age exposed in a small area including Chico Creek, Butte Creek, Mill Creek, Deer Creek, Pence (or Pentz) Ranch, and Tuscan Springs.

BIBLIOGRAPHY ANDERSON, F. M., 1902, "Cretaceous Deposits of the Pacific Coast," Proc. California Acad. Sci., Ser. Ill, Vol. II, No. I, pp. 1-154. TEST SIDE OF MOLI.USCAN ZONAL CHARACTERISTIC AMMONITES 5ANTA ANA SACRAMENTO VALLEY FROM CHICO, BUTTE, MILL. REDDING AREA, INniCF? IN CALIFORNIA MOUNTAINS, CORNDJG TO VACAVILLE, AND DEER CREEKS; CALIFORNIA (After Popenor 1942) AMD OREGON CALIFORNIA CALIFORNIA PENTZ RANCH, (Section aftel Popenoc 1943) of Kirby (1942, 1943) CALIFORNIA TVTTZ,

MAKSTRICHTIAN

Not identified liihologically

SANTONIAN-

Yolo Baker Canyon forma tic If conglomerate Traf^odestnoctras

Tratiuco formal Upper p; Venadt

r_ EN OMAN! AN

FIG. 4.—Correlation of some Upper Cretaceous sections in California and Oregon. 1984 DALLAS L. PECK, ET AL.

1931, "Upper Cretaceous (Chico) Deposits in Siskiyou County, California," in AVERILL, C. v., "Preliminary Report on Economic Geology of the Shasta Quadrangle," California Div. Mines, Vol. 27, pp. 11-14. 1943, "Synopsis of the Later Mesozoic in California," California Dili. Mines Bull. 118, pp. 183-86. COBBAN, W. A., AND REESIDE, J. B., JR., 1952, "Correlation of the Cretaceous F'ormations of the Western Interior of the United States," Btdl. Geol. Soc. America, Vol. 63, pp. 1011-44; 2 figs., I pi. DiLlER, J. S., 1893, "Cretaceous and Karly Tertiary of Northern California and Oregon," ibid., Vol. 4, pp. 205-24. , AND KAY, G. F., 1924, "Riddle, Oregon," U. S. Geol. Suri'ey Geol. Atlas Folio 21S, pp. 3-4. DUNN, R. L., i8()4, "Tlie Auriferous (Conglomerate in California," California Stale Min. Bur. Rept. i^2,PP-459-71- GABB, W. M., 1869, as reported by J. D. WHITNEY, California Geol. Survey, Paleontology, Vol, 2, p. XIV and footnote p. 129. GILBERT, C. M., 1954, in WILLIAMS, H., TURNER, F. S., AND GILBERT, C. M., Petrography, pp. 292-93. W. H. Freeman and Company, San Francisco. MATSUMOTO, TATSURO, ET AL., 1953, "The Cretaceous System in the Japanese Islands," Japanese .Soc. Promotion Sci. Research, pp. 1-242, Figs. 1-46; 36 tables, Pis. 1-16. MATSUMOTO, TATSURO, 1953, "Selected Cretaceous Leading Ammonites in Hokkaido and Saglialien," published as an appendix to "The Cretaceous System in the Japanese Islands," ibid., pp. 243- 324, Figs. 47-77, Pis- 17-36. I^OPENOE, W. p., 1942, "Upper Cretaceous Formations and F'aunas of Southern California," Bull. Amer. Assoc. Petrol. Geol., Vol. 26, No. 2, pp. 162-87; 4 figs. , 1943, "Cretaceous: East Side Sacramento Valley, Sliasta and Butte Counties, California," ibid., Vol. 27, No. 3, pp. 306-12; 2 figs. SPATH, ]J. F., 1953, "Tire Upper Cretaceous Cephalopoda Fauna of Graham Land," Falkland Islands Dependencies Siirvey Scientific Reports, No. 3, pp. 1-60; 13 pis. TURNER, H. W., 1903, "The Cretaceous Auriferous Conglomerate of the Cottonwood Mining District, Siskiyou County, California," Eng. and Min. Jour., Vol. 76, pp. 653-54. UsHUR, J. L., 1952, "Ammonite Faunas of the Upper Cretaceous Rocks of Vancouver Island, British Columbia," Geol. Survey Canada Bull. 21. 182 pp., 4 figs., 3 tables, 31 pis. WELLS, F. G., 1939, "Preliminary Geologic Map of tlie Medtord Quadrangle, Oregon," Oregon Dept. Geology and Min. Industries. WILLIAMS, HOWEL, 1949, "Geolog\- of the Macdoel Quadrangle," California Div. Mines Ball, iji, pp. 16-18; PI. IV. WRIGHT, C. W., 1953, "Notes on Cretaceous Ammonites. I. Scaphitidae," Annals and Mag. Nat.Hist., Ser. 12, Vol. 6, pp. 473-76. , AND MATSUMOTO, TATSURO, 1954, "Some Doubtful Cretaceous Ammonite Genera from Japan and Saghalien," Mem. Faculty Sci. Kyushu Univ., Ser. D, Geology, Vol. 4, No. 2, pp. 107-34, Figs. 1-22.