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Davy Crockett fault

Pilot Mountain fault

Baker Spring monocline

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Mill Creek fault

Mill Creek graben

St. Joe fault

Confederate fault

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Figure 5. Photograph of (A) quartz crystals on chert block from 

Boone Formation (pencil is about 5 in. long), and (B) chert breccia 

mass (hammer handle is about 12 in. long). Photographs by M.R. 

Hudson and K.J. Turner, 2008.

A

B

Figure 4. Structural data from the St. Joe 

quadrangle. Number of data are “n”. (A) Rose 

diagram of strike frequency (left) and stereoplot 

of poles and orientation density contours (right) 

for faults in quadrangle. Contour levels are 

multiples of standard deviations. (B) Subset of 

striated faults with known slip sense that are 

compatible with normal (left) and strike-slip (right) 

paleostress regimes. Arcs and dots are lower 

hemisphere projections of fault planes and their 

slip lines, respectively. Small arrows show 

movement sense of hanging wall block. Open 

five-, four-, and three-pointed stars represent 

orientation of maximum, intermediate, and least 

principal paleostress axes, respectively, from 

analysis of Angelier (1990). Large white arrows 

show azimuth of least horizontal compression. 

(C) Rose diagram of strike frequency of joints 

recorded within the map area. 

N

n = 625

N

n = 19 Strike-slip faults

N

Normal faults n = 15

N N

n = 97

A

B

C

Figure 3. Shaded-relief digital elevation map of quadrangle with locations of Pb-Zn mines and prospects, structural features, and sites 

where faults (squares) and silicification (triangles) were observed. Where determined, slip senses for faults at sites are indicated as normal, 

N (rake 90° to 60°); oblique, O (rake 59° to 30°); and strike-slip, S (rake 29° to 0°). Sites with silicification define an elongate area (pink) 

centered mostly north of the St. Joe and Davy Crockett faults. Silicification was classified as Q, coarse and microcrystalline quartz 

crystals; B, silica-cemented chert breccia; or C, enhanced silica cementation in sandstone. Mine and prospect locations are estimated 

from descriptions in McKnight (1935).

S S

S

O S

S

S S

N N S,O,N

N

N

N

N

N

N

S

S

S

S

B B

B

Q

Q

Q

Q

Q

Q Q Q

Q

Q

C

C

C

C

C

36°7'30"

92°52'30" 92°45'

36°

Anticline

Silicification site

EXPLANATION

Fault site

Mine or prospect site

Syncline

Monocline

Fault—Dashed where approximately

 located, dotted where concealed

Figure 2. Stratigraphic column for Paleozoic rocks representative of the map area. Provincial series are from 

Purdue and Miser (1916) and McFarland (1988).

BOONE

FORMATION

EVERTON

FORMATION

BATESVILLE SANDSTONE

St. Joe Limestone Member

ORDOVICIAN MISSISSIPPIAN PENNSYLVANIAN

(part)

FERNVALE LIMESTONE

MeramecianOsagean Osagean- Kinderhookian

SYSTEM

PROVINCIALSERIES

PLATTIN LIMESTONE

CASON SHALE

ST. PETER SANDSTONE

Newton Sandstone Member

Upper part Lower part

Mohawkian Whiterockian Chesterian Morrowan

Cincinnatian

FAYETTEVILLE

SHALE

PITKIN LIMESTONE

Wedington Sandstone Member

Cane Hill Member

Prairie Grove Member

Upper part BLOYD

FORMATION

HALE

FORMATION

Lower part

METERS

200

400

600

800

1000

1200

1400

1600

500

400

300

200

100

0 0

FEET

Sandstone

Shale, siltstone

Limestone

Dolomite

Chert

Unconformity

Crossbedded sandstone

EXPLANATION

Figure 1. Location of study area within northern Arkansas, adjacent to the western part of Buffalo National River. Other U.S. 

Geological Survey geologic maps in area (Hudson, 1998; Hudson and others, 2001, 2006; Hudson and Murray, 2003, 2004; Hudson 

and Turner, 2007) are listed by publication number. Lower regional map illustrates geological and selected physiographic provinces of 

Arkansas and adjacent areas. 

Harrison

Jasper

Buffalo

River

36°

36°15'

35°52.5'

36°7.5'

 93°15'

 93°30' 92°45'

93°

Buffalo

National

43 7

65

0 5 KILOMETERS

River

MF 2356

OFR 98–116

MF 2412

OSAGE NE

OSAGE SW

GAITHER HARRISON

JASPER WESTERN GROVE

BOXLEY MURRAY MT. JUDEA EULA

HASTY

PARTHENON

PONCA ST. JOE MAUMEE

MARSHAL

SIM 2847 SIM 2921 THIS STUDY

SIM 2991

Ozark Dome

94° 92° 90°

Mississippi Embayment

Arkoma Basin

St. Francois

Mountains

Salem 

Plateau

Plateau

Cretaceous

 rocks

Springfield

37°

35°

33°

KANSAS

MISSOURI

TEXAS

ARKANSAS

TENNESSEE

MISSISSIPPI

OKLAHOMA

SNOWBALL

Ouachita Mountains

Boston Mountains

Mp

Mfw

Mf

Mbv

Qal

Mb

Mbs

Unconformity

Unconformity

Qc

Unconformity

bu

bl

hg

hc

Unconformity

Unconformity

Of

Ou

Unconformity

Unconformity

Unconformity

Unconformity

Unconformity

Oeu

Opl

Osp

Oel

CORRELATION OF MAP UNITS

QUATERNARY

MISSISSIPPIAN

PENNSYLVANIAN

ORDOVICIAN

Chesterian

Morrowan

Meramecian–Osagean

Osagean–Kinderhookian

Lower Ordovician

Middle Ordovician

Upper Ordovician

Mf

Mbv

Mb

Mbs

Opl

Of

Osp

Oeu

Oel

Ou

Contact

Line of equal elevation showing base of Boone Formation,

 contour interval 50 ft 

Control point showing elevation in feet on base or

 top of Boone Formation 

Cason Shale locality

Fault—Dashed where approximately located

Normal fault—Dashed where approximately located, 

 dotted where concealed, bar and ball on downthrown block 

Strike-slip fault, right-lateral offset—Dashed where 

 approximately located, arrows show relative motion

Anticline

Fault movement—Away from viewer (left), toward viewer (right),

 shown in cross sections only

Syncline

Monocline

Strike and dip of bedding

Inclined

Horizontal

51

MAP EXPLANATION

900

900

 INTRODUCTION

This map summarizes the geology of the St. Joe 7.5-minute quadrangle (fig. 1) in the 

Ozark Plateaus region of northern Arkansas. Geologically, the area lies on the southern 

flank of the Ozark dome, an uplift that exposes oldest rocks at its center in Missouri. 

Physiographically, the St. Joe quadrangle lies within the Springfield Plateau, a topographic 

surface generally held up by Mississippian cherty limestone (Purdue and Miser, 1916). The 

quadrangle also contains isolated mountains (for example, Pilot Mountain) capped by 

Pennsylvanian rocks that are erosional outliers of the higher Boston Mountains plateau to 

the south. Tomahawk Creek, a tributary of the Buffalo River, flows through the eastern part 

of the map area, enhancing bedrock erosion. Exposed bedrock of this region comprises an 

approximately 1,300-ft-thick sequence of Ordovician, Mississippian, and Pennsylvanian 

carbonate and clastic sedimentary rocks (fig. 2) that have been mildly deformed by a series of 

faults and folds. 

The geology of the St. Joe quadrangle was mapped by McKnight (1935) as part of a 

larger area at 1:125,000 scale. The current map confirms many features of this previous 

study, but it also identifies new structures and uses a revised stratigraphy. Mapping for this 

study was conducted by field inspection of numerous sites and was compiled as a 1:24,000-

scale geographic information system (GIS) database. Locations and elevations of sites were 

determined with the aid of a global positioning satellite receiver and a hand-held barometric 

altimeter that was frequently recalibrated at points of known elevation. Hill-shade-relief and 

slope maps derived from a U.S. Geological Survey 10-m digital elevation model as well as 

U.S. Geological Survey orthophotographs from 2000 were used to help trace ledge-forming 

units between field traverses within the Upper Mississippian and Pennsylvanian part of the 

stratigraphic sequence. Strikes and dips of beds were typically measured along stream 

drainages or at well-exposed ledges. Beds dipping less than 2° are shown as horizontal. 

Structure contours constructed on the base of the Boone Formation were hand drawn based 

on elevations of control points on both lower and upper contacts of the Boone Formation as 

well as other limiting information on their maximum or minimum elevations.

DESCRIPTION OF MAP UNITS

Alluvial deposits (Quaternary)—Unconsolidated sand and gravel of Tomahawk, Mill, and Dry Creeks. Active-channel gravel deposits composed of 

subangular to rounded Paleozoic rock clasts of mixed lithology along 

drainages are interspersed with bedrock exposures (not mapped). Low 

terraces of light-brown, fine sand are locally present adjacent to creeks. As 

thick as 10 ft

Colluvial deposits (Quaternary)—Unconsolidated deposits of subrounded to 

angular blocks as large as 20 ft in diameter, commonly in an orange-brown 

silty clay matrix. Blocks are mostly derived from basal sandstone of upper 

part of Bloyd Formation (bu) and Cane Hill Member (hc) of the Hale 

Formation. Deposits have fan-like morphology and were mapped where 

sufficiently thick to mask typical ledge-flat topography of underlying 

bedrock. Smaller, thinner colluvial deposits elsewhere were not mapped. 

Thickness uncertain but probably more than 10 ft 

Bloyd Formation (Lower Pennsylvanian, Morrowan)—Interbedded sequence 

of sandstone, siltstone, shale, and thin limestone beds separated into lower 

and upper intervals. As much as 180 ft thick

Upper part—Crossbedded sandstone capping Pilot and St. Joe Mountains. 

Sandstone forms prominent cliffs as tall as 60 ft on Pilot Mountain and 

more subdued ledges on St. Joe Mountain. Sandstone is white to 

light-brown, fine- to medium-grained quartz arenite and is a composite of 1- 

to 3-ft-thick tabular and trough crossbed sets. Sandstone has a sharp 

erosional base and contains concentrations of white quartz pebbles and, 

locally, casts and molds of wood fragments. Rocks of the upper Bloyd 

Formation were originally assigned to the Winslow Formation by Purdue 

and Miser (1916). Zachry (1977) concluded that the basal sandstone was a 

time-equivalent unit with the Woolsey Member of the Bloyd Formation 

farther west and designated it the “middle Bloyd sandstone.” Maximum 

preserved thickness is 110 ft

Lower part—Sequence of predominantly dark-gray to black shale and 

siltstone with thin beds of sandstone and limestone; poorly exposed under 

moderate to steep hillslopes. Siltstone is medium to dark gray, fissile, and 

moderately bioturbated. Medium beds of rippled, very fine grained 

sandstone are locally exposed as ledges. Coarse bioclastic limestone is 

reddish gray and weathers dark brown but is poorly exposed and mostly 

observed in loose blocks in lower part of sequence. Thickness 50–70 ft

Hale Formation (Lower Pennsylvanian, Morrowan)—Interbedded sequence 

of sandstone, siltstone, shale, and thin limestone. Thickness 100–180 ft

Prairie Grove Member—Brown to reddish-brown, fine- to medium-grained, 

thick-bedded, calcite-cemented sandstone. Locally contains quartz pebbles 

in its base and thin interbeds of fossiliferous limestone. Beds are planar or 

crossbedded, and crossbeds may have bi-directional dips. Weathered 

sandstone forms rounded surfaces. Sandstone forms steep hillslopes or 

ledges that are commonly covered by slope debris from overlying units. 

Thickness 10–25 ft

Cane Hill Member—Interbedded sequence of shale, siltstone, and 

sandstone. Most of unit is poorly exposed dark-gray fissile shale and 

thin-bedded siltstone that form gentle to moderately steep slopes. Upper 

part locally contains rippled, thin-bedded, very fine and fine grained 

sandstone intervals as thick as 5 ft. Lower part includes 10-ft-thick 

sandstone interval that changes downward from olive-brown, very fine 

grained, thin-bedded sandstone with ripple cross-lamination to reddishbrown, medium- to thick-bedded, very fine grained to medium-grained 

sandstone with trough crossbeds. Lower sandstone contains sparse casts of 

wood fragments and conglomerate lenses with quartz pebbles and angular 

to subrounded clasts of shale, siltstone, and sandstone. Unit unconformably 

overlies the Pitkin Limestone. Thickness varies from 60 ft to as much as 

200 ft on east side of Pilot Mountain

Pitkin Limestone (Upper Mississippian, Chesterian)—Generally medium- to 

dark-gray, fetid limestone. Limestone in medium to thick wavy beds varies 

from micrite at base to coarse grained and locally oolitic near top. Limestone beds may contain abundant crinoids, brachiopods, corals, and 

bryzoan Archimedes. Basal contact with Fayetteville Shale is conformable, 

although rarely exposed. Pitkin generally forms a prominent ledge or steep 

slope. Thickness 40–80 ft

Fayetteville Shale (Upper Mississippian, Chesterian)—Fine-grained 

sandstone and siltstone of Wedington Sandstone Member that grades 

downward into main body of black, slope-forming shale. Thickness 

160–200 ft

Wedington Sandstone Member—Brown to light-gray, well-indurated, 

calcite-cemented sandstone and siltstone. Wedington caps a steep slope 

and is separated from overlying Pitkin Limestone by a common 

topographic bench. Sandstone is very fine grained and is present in thick 

to thin planar beds with internal parallel laminations and locally developed 

low-angle crossbeds. Sandstone grades downward into siltstone beds that 

are ripple cross-laminated and bioturbated. Wedington grades downward 

into main body. Thickness 25–40 ft 

Main body—Below the Wedington Sandstone Member, middle part of 

Fayetteville Shale is poorly exposed black shale that locally contains thin, 

rippled beds of olive-brown siltstone near its top. Lower part of Fayetteville 

crops out along stream gullies where it consists of black fissile shale that 

may contain medium- to light-gray, fetid septarian concretions as 

large as 2 ft in diameter. The Fayetteville Shale is susceptible to landslides. 

Thickness 130–160 ft

Batesville Sandstone (Upper Mississippian, Chesterian)—Fine-grained to 

very fine grained, light- to medium-brown, calcite-cemented sandstone with 

sparse interbedded limestone. Thin to medium beds are typically parallel 

laminated; low-angle crossbeds common in upper part of unit. Sandstone 

commonly contains burrows on bedding plane surfaces. Sandstone breaks 

into thin flat blocks. One or more discontinuous, 1- to 3-ft-thick, mediumto dark-gray, fetid, fossiliferous limestone beds are locally interbedded with 

sandstone; limestone beds contain crinoids and brachiopods. Both 

sandstone and limestone beds may contain 2- to 10-mm-diameter oxidized 

pyrite framboids that weather to reddish-brown spheres. Where stripped of 

overlying Fayetteville Shale, top of Batesville forms topographic flats. Unit 

hosts sinkholes formed by collapse into dissolution cavities in underlying 

Boone Formation. Thickness 40–60 ft

Boone Formation (Upper to Lower Mississippian)—Limestone and cherty 

limestone of main body that grade into the basal St. Joe Limestone 

Member. The Boone Formation is a common host of caves and sinkholes. 

Total thickness is 380–405 ft 

Main body (Upper to Lower Mississippian, Meramecian to Osagean)— 

Medium- to thick-bedded, chert-bearing bioclastic limestone. Limestone is 

light to medium gray on fresh surfaces and generally coarsely crystalline 

with interspersed crinoid ossicles. A 1- to 3-ft-thick bed of oolitic limestone 

is common in upper part of unit. Beds of dense, fine-grained limestone are 

present in upper one-third of unit. Beds are typically parallel planar to 

wavy, but channel fills are locally present in lower part of unit. Chert 

content varies vertically and laterally within Boone and forms lenticular to 

anastomosing lenses. Chert-rich horizons are generally poorly exposed but 

produce abundant float of white-weathered chert on hillslopes. Chert in 

uppermost part of unit contains prominent brachiopod molds. Thickness 

310–375 ft 

St. Joe Limestone Member (Lower Mississippian, Osagean to 

Kinderhookian)—Thin and wavy bedded bioclastic limestone containing 

ubiquitous 3- to 6-mm-wide crinoid fragments in a finely crystalline matrix. 

Limestone is commonly pink to red on fresh surfaces due to hematite in 

matrix, but color varies depending on hematite concentration. Lenticular 

red to pink chert nodules are locally present in upper part. Contact with 

overlying main body of Boone Formation is gradational and marked by 

increase in chert and thicker beds upward. Middle to lower part of St. Joe 

Limestone Member contains greenish-gray shale interbeds. Base of St. Joe 

is a 0.3- to 8-ft-thick, very fine to fine-grained, moderately sorted, tan 

sandstone containing phosphate pebbles. Base of unit is an important 

unconformity that variably truncates Fernvale Limestone, Plattin Limestone, 

St. Peter Sandstone, or upper part of the Everton Formation in various 

parts of quadrangle. Total thickness of member is 20–50 ft

Fernvale Limestone (Upper Ordovician)—Thick- to massive-bedded, coarsely 

crystalline bioclastic limestone. Limestone is light gray to pink on fresh 

surfaces and contains abundant 3- to 10-mm-wide cylindrical to barrelshaped crinoid ossicles in a coarsely crystalline matrix. Mapped undivided 

with Fernvale Limestone is a 5-ft-thick fissile to massive black to blue-green 

shale with 1 to 2 in. black phosphate pebbles, which is assigned to Cason 

Shale (Upper Ordovician) where it was observed beneath a cliff of St. Joe 

Limestone Member adjacent to Mill Creek (NE1/4, NE1/4, Sec. 18, T. 16 

N., R. 17 W.). Unit is exposed in eastern Mill Creek graben where it is as 

thick as 20 ft

Plattin Limestone (Middle Ordovician)—Thin- to medium-planar-bedded, 

fine-grained, dense limestone locally interbedded with calcarenite. Characteristically, dense, very fine grained, medium-gray limestone that breaks 

with conchoidal fracture and weathers to very light gray, thin, tabular 

blocks. Locally in upper parts there are interbeds of laminated, tan to 

light-gray, fine-grained to very fine grained, limey to dolomitic calcarenite as 

thick as 10 ft; calcarenite has fetid odor when freshly broken. Thickness 

ranges from 40 ft in southwestern part of area to nothing in northwestern 

parts due to pre-Mississippian erosion beneath unconformity at base of St. 

Joe Limestone Member of Boone Formation

St. Peter Sandstone (Middle Ordovician)—Very fine grained, grayish-yellow 

sandstone interbedded with blue-green siltstone, shale, and sparse dolostone. Sandstone is calcite-cemented arenite containing well-rounded quartz 

grains. Upper part of unit, as thick as 25 ft, is sandstone interbedded with 

blue-green fissile shale, thin-bedded siltstone, and sparse 0.5- to 3-ft-thick 

beds of brown-gray, fine crystalline dolostone; shale, siltstone, and 

dolostone interval poorly exposed, but is locally marked by zone of slumped 

sandstone blocks on hill slopes. Main part of unit contains a sequence of 1- 

to 2-ft-thick sandstone beds overlying a massive basal sandstone ledge as 

thick as 20 ft. Bioturbation is common in most sandstone beds and 

includes cylindrical burrows (Skolithos) perpendicular to bedding that 

weather to distinctive straw-like forms. Basal sandstone is crossbedded, 

contains inclined fractures, and discordantly overlies laminated sandy 

dolomite in upper part of Everton Formation at local recesses. Unit thins 

to nothing to northwest due to pre-Mississippian erosion beneath unconformity at base of St. Joe Limestone Member of Boone Formation. Thickness 

ranges from 0 to 70 ft

Everton Formation (Middle Ordovician)—Interbedded dolostone, limestone, 

and sandstone sequence, divided into upper and lower parts. Unit is 

300–400 ft thick

Upper part—Interbedded dolostone, sandstone, and limestone. Limestone is 

finely crystalline, light gray, thick bedded, and locally fossiliferous, and is 

present in intervals as thick as 20 ft. Dolostone is light to dark gray, finely 

to medium crystalline, laminated, and medium to thick bedded commonly 

containing sandstone stringers. Sandstone is arenite composed of 

well-sorted, well-rounded, fine to medium quartz grains. Sandstone is light 

tan to white in planar, medium to thick beds and is variably cemented by 

dolomite or calcite; sandstone locally grades into sandy dolostone or 

limestone. Limestone interbedded with limy sandstone and lesser dolostone 

at top of unit comprises Jasper Member of Glick and Frezon (1953). 

Jasper Member is up to 40 ft thick but has been removed in northwestern 

part of quadrangle due to pre-Mississippian erosion. Dolostone and 

dolomitic sandstone underlying Jasper Member make up most of upper 

part of Everton. Base of upper part of Everton is marked by base of 

Newton Sandstone Member (McKnight, 1935), a planar, medium-bedded 

quartz arenite composed of well-sorted, well-rounded, fine to medium 

quartz grains. Newton Sandstone Member is 5–10 ft thick. Upper part of 

Everton Formation is 180–200 ft thick 

Lower part—Interbedded dolostone, sandstone, and limestone. Limestone is 

restricted to upper part of unit and is interbedded with dolostone and 

sandstone. Limestone is light gray, finely crystalline, thin to medium 

bedded, commonly laminated, and contains sparse stromatolite 

hemispheres as large as 1 ft in diameter. Dolostone, present throughout 

unit, is light gray to grayish brown, finely to medium crystalline, thin to 

thick bedded, and commonly laminated, and it commonly contains stromatolites. Sandstone is light-tan to white quartz arenite, composed of 

well-sorted, well-rounded, fine to medium grains, variably cemented by 

dolomite or calcite. Sandstone intervals, composed of planar, thin to 

medium beds as thick as 6 ft, are present throughout unit. Sandstone also 

forms lenses and stringers within limestone and dolostone intervals. Lightto dark-brownish-gray dolostone and sandy dolostone interspersed with 

sandstone are predominant in lower part of unit. Collapse breccia with 

clasts of planar laminated dolomite and dolomitic sandstone is present. 

Unit is 250 ft thick where fully exposed near Mt. Hersey to the westsouthwest on the Western Grove quadrangle (Glick and Frezon, 1953) but 

only upper 60 ft is exposed within St. Joe quadrangle

Lower Ordovician rocks, undivided—Sedimentary rocks shown on cross 

section only

STRATIGRAPHY

The quadrangle preserves a 1,300-ft-thick record of early and late Paleozoic deposition 

on what is now the southern margin of the North American continent. Provincial series 

terms for Pennsylvanian and Mississippian units are from McFarland (1988).

The Middle Ordovician Everton Formation (Oe) is a heterogeneous sandstone and 

carbonate unit that Suhm (1974) interpreted to have been deposited in barrier island and 

tidal flat depositional environments. The Everton Formation is discontinuously overlain by 

the Middle Ordovician St. Peter Sandstone (Osp) and Plattin Limestone (Opl) and, in the 

eastern part of the Mill Creek graben, by the Upper Ordovician Fernvale Limestone (Of) and 

Cason Shale (McKnight, 1935). Due to its limited thickness and distribution, Cason Shale 

was mapped undivided with Fernvale Limestone where it was observed west of the town of 

St. Joe. Whereas Cason Shale includes Silurian facies in its type area to the east near 

Batesville, Arkansas, Craig (1975) demonstrated that only its basal Upper Ordovician part is 

present in its isolated western outcrops. 

The base of the Mississippian section is a major unconformity that progressively cuts 

deeper into the underlying Ordovician section towards the northwestern part of the 

quadrangle. The Mississippian Boone Formation (Mb) is the most widespread unit at the 

surface within the quadrangle. The phosphate-nodule-bearing sandstone at the base of the 

St. Joe Limestone Member (Mbs) is persistent throughout much of northern Arkansas 

(McKnight, 1935). This sandstone was probably deposited as a transgressive lag during 

sea-level rise in Late Devonian time (Horner and Craig, 1984). The contact of the main 

body of the Boone Formation with the St. Joe Limestone Member is gradational and is 

based on the change to thin bedding and the generally chert-free lithology of the St. Joe 

Limestone Member. Near the top of the formation an oolite interval as thick as 3 ft is 

common. Braden and Ausbrooks (2003a) also recognized this facies in areas to the south 

and correlated this interval with the Short Creek Oolite Member of the Boone Formation, 

which is present in Missouri and Kansas (McKnight and Fischer, 1970). Black shales of the 

Fayetteville Shale (Mf) represent deposition within a southward-deepening muddy shelf that 

shoaled upward during deposition of the Pitkin Limestone (Mp) (Handford, 1985).

Initial Morrowan deposition reflects sea-level rise following a sea-level drop at the end of 

the Mississippian (Sutherland, 1988). Typical thin-bedded, rippled, fine- to very fine grained 

sandstones and siltstones of Cane Hill Member (hc) of the Hale Formation were probably 

deposited in tidal flat environments (Manger and Sutherland, 1992). The quadrangle lies at 

the northeastern margin of the distribution of thick Prairie Grove Member (hg) of the Hale 

Formation (Sutherland, 1988). The Prairie Grove Member in the study area is represented 

by indistinct planar- or cross-bedded, calcite-cemented sandstone deposited in a shoreface 

environment. The lower part of the Bloyd Formation (bl) conformably overlies the Prairie 

Grove Member and represents deposition in an open-marine platform setting as sea level 

continued to rise. Pennsylvanian sandstone and shale of the upper part of the Bloyd 

Formation (bu) were originally called Winslow Formation by Purdue and Miser (1916), 

with the basal Greenland Sandstone Member of the Atoka Formation (Henbest, 1953) 

representing the prominent cliff-forming crossbedded sandstone. Zachry (1977), however, 

concluded that the cliff-forming sandstone was a time-equivalent unit with the Woolsey 

Member of the Bloyd Formation farther west and designated it with the informal term 

“middle Bloyd sandstone.” The unconformable contact between the upper and lower parts 

of the Bloyd Formation represents a period of erosion prior to deposition of the middle 

Bloyd sandstone by terrestrial braided streams. 

STRUCTURAL GEOLOGY

Rocks within the map area were deformed by a system of faults and folds. Structure 

contours on the base of the Boone Formation illustrate the location of structures and their 

vertical offset. The structure contours conform to elevations at 328 control points located at 

both lower and upper contacts of the Boone Formation, as well as other information limiting 

maximum or minimum elevations of these contacts. A 390-ft thickness for the Boone 

Formation (Mb) (including the St. Joe Limestone Member (Mbs)) was used to project the 

elevation of the basal contact from points on the upper contact. This average thickness was 

based on thicknesses from five stratigraphic sections farther west near the Buffalo River 

(Hudson, 1998). 

Several regionally extensive fault systems intersect within the St. Joe quadrangle. We 

map faults that correspond to those previously named by McKnight (1935) as the St. Joe, 

Mill Creek, Pilot Mountain, Tomahawk, and South Tomahawk faults, although our fault 

traces differ in detail, and we also map several additional faults. The Mill Creek graben in 

the southwestern part of the quadrangle is part of a graben system that extends about 15 

miles farther to the west (Purdue and Miser, 1916; Hudson and Murray, 2003; Hudson and 

others, 2006). Bounding the south side of the graben, the Mill Creek fault dies out eastward 

at its intersection with the northeast-striking Confederate fault, which we project into the 

quadrangle from areas farther southwest (Braden and Ausbrooks, 2003a, 2003b). Structure 

contours highlight a gentle southeast dip of strata in a broad flank northwest of the Confederate fault. This dipping block was part of the St. Joe monocline as named by McKnight 

(1935), but we abandon this as a separate structural feature and instead link it to growth of 

the Confederate fault. Cross section A–A’ demonstrates that about 200 feet down-to-thesoutheast throw on the Confederate fault is required in addition to the southeast dip of strata 

to provide sufficient structural relief for the typical thickness of Boone Formation (Mb) 

between outcrops of its base and top. Bounding the north side of the Mill Creek graben, the 

St. Joe fault continues northeastward from its intersection with the Confederate fault until it 

overlaps the Davy Crockett fault at the southeastern border of Sec. 8, T. 16 N., R. 17 W. 

The Davy Crockett fault includes the northeast-striking segment of the Tomahawk fault of 

McKnight (1935), but we rename this fault segment because our mapping demonstrates that 

it continues to the northeast past McKnight’s west-northwest striking segment of the 

Tomahawk fault, which we retain as a name. Similar to the Tomahawk fault, the westnorthwest-striking South Tomahawk and Pilot Mountain faults extend from beyond the east 

edge of the quadrangle to intersect the Davy Crockett fault at their west ends. The West 

Mountain fault aligns with, and may be a westward continuation of, the Pilot Mountain fault 

across the Davy Crockett fault.

Whereas the vertical offset of structures can be estimated from the elevation difference 

of formation contacts across the structures, their lateral offset is difficult to measure due to 

the lack of appropriate markers. Fault data collected from mostly small-scale faults at 

numerous sites within the quadrangle (fig. 3) indicate the typical orientations and slip senses 

for faults (fig. 4A) and give insight into the causative stresses responsible for deformation. 

Most of these faults are small displacement cataclastic faults, deformation bands (Aydin and 

Johnson, 1978), preferentially developed in sandstones of the St. Peter Sandstone (Osp) 

and Everton Formation (Oe). Those faults whose slip senses could be determined are 

predominantly normal or strike slip (fig. 4B). Normal faults strike from east-northeast to 

east-southeast and dip moderately to the north or south. Among strike-slip faults, those with 

right-lateral sense mostly strike northeast and those with left-lateral sense have strikes 

ranging from east-southeast to south-southeast. Paleostress inversions for these normal and 

strike-slip faults, using the method of Angelier (1990), demonstrate that they formed in a 

stress regime with a least principal stress axis oriented south to south-southeast and near 

horizontal and with intermediate and maximum principal stress axes flipping between near 

vertical and east-northeast and near horizontal (fig. 4B). Similar coordinated movements 

among normal and strike-slip faults have been documented elsewhere in the southern Ozark 

dome, and their north-south extension accommodated late Paleozoic flexure of the southern 

continental margin as it was loading by the adjacent Ouachita orogenic belt (Hudson, 2001). 

From these data we interpret that (1) northeast-striking Confederate and Davy Crockett 

faults have components of right-lateral slip as well as down-to-the-southeast throw, and (2) 

east- to southeast-striking faults like those bounding the Mill Creek graben have normal slip. 

The structure contours illustrate several folds and broad domes. The Baker Spring 

monocline on the eastern edge of the quadrangle has about 150 ft of relief and is expressed 

by consistent 5–10° north to north-northeast dips. Just to the north, a synclinal axis 

underlies St. Joe and Pilot Mountains with a northern limb upturned adjacent to the Davy 

Crockett (cross section B–B’ ) and Pilot Mountain faults. Two east-west-trending open 

anticlines and a syncline lie directly north of the St. Joe fault. A broad, east-southwesttrending dome is present in the northeastern part of the quadrangle. Away from folds, dips 

of bedding are low and variable in direction. These dispersed attitudes are attributed in part 

to local subsidence caused by karst dissolution within the abundant limestone and dolostone 

rock units. 

Joints measured within the map area (695 total) are near vertical and distributed in 

several sets (fig. 4). The dominant set strikes north. Less prominent joint sets strike 

northeast and west-northwest. Joint planes within limestone and dolostone formations, such 

as the Boone (Mb) and Everton Formations (Oe), are commonly enlarged due to dissolution.

ECONOMIC GEOLOGY

McKnight (1935) described lead and zinc ores from several mines in the St. Joe and 

Tomahawk Creek mining districts located on the northern, upthrown side of the St. Joe and 

Davy Crockett faults within the St. Joe quadrangle (fig. 3). The dominant ore mined from 

local prospects consists of sphalerite (ZnS) and zinc carbonate and minor copper in the form 

of malachite. Dolomitic and limestone layers of the Everton Formation (Oe) host most 

prospects. Silicification was commonly associated with Pb-Zn mineralization (McKnight, 

1935) and was noted at several sites during this field investigation (fig. 3) defining an 

elongate area mostly north of the St. Joe and Davy Crockett faults. Within the Boone 

Formation (Mb), silica was precipitated as fracture coatings of drusy quartz having euhedral 

crystals tips as wide as 1⁄2 in. (fig. 5A). Additionally, within the Boone Formation and its 

basal St. Joe Limestone Member, several elongate bodies of brecciated chert cemented by 

microcrystalline quartz (fig. 5B) were noted, standing 3 to 20 ft high as erosion-resistant 

ridges. These masses probably formed by dissolution of limestone and collapse of chert 

within the Boone Formation followed by silicification during flow of mineralizing fluids. 

Enhanced silicic cementation of sandstone beds was also noted within the Ordovician St. 

Peter Sandstone (Osp) and Everton Formation (Oe) and at one location within the Pennsylvanian Cane Hill Member (hc) of the Hale Formation. 

ACKNOWLEDGMENTS

This work was conducted in a cooperative project between the U.S. Geological Survey 

and the U.S. National Park Service. Special thanks go to the many private owners who 

allowed access onto their land during this study. 

REFERENCES CITED

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III, A new rapid direct inversion method by analytical means: Geophysical Journal 

International, v. 103, p. 363–376.

Aydin, A., and Johnson, A.M., 1978, Development of faults as zone of deformation bands 

and as slip surfaces in sandstone: Pure and Applied Geophysics, v. 116, p. 931–942.

Braden, A.K., and Ausbrooks, S.M., 2003a, Geologic map of the Eula quadrangle, Newton 

and Searcy Counties, Arkansas: Arkansas Geological Commission Digital Geologic 

Quadrangle Map DGM-AR-00269, scale 1:24,000.

Braden, A.K., and Ausbrooks, S.M., 2003b, Geologic map of the Snowball quadrangle, 

Searcy County, Arkansas: Arkansas Geological Commission Digital Geologic Quadrangle Map DGM-AR-00800, scale 1:24,000.

Craig, W.W., 1975, Stratigraphy and conodont faunas of the Cason Shale and the Kimmswick and Fernvale Limestones of northern Arkansas, in Headrick, K.N., and Wise, 

O.A., eds., Contributions of the geology of the Arkansas Ozarks, Arkansas Geological 

Commission, p. 61–95. 

Glick, E.E., and Frezon, S.E., 1953, Lithologic character of the St. Peter Sandstone and 

Everton Formation in the Buffalo River Valley, Newton County, Arkansas: U.S. 

Geological Survey Circular 249, 39 p.

Handford, C.R., 1985, Facies and bedding sequences in shelf-storm-deposited carbonates— 

Fayetteville Shale and Pitkin Limestone (Mississippian), Arkansas: Journal of Sedimentary Petrology, v. 56, p. 123–137.

Henbest, L.G., 1953, Morrow Group and lower Atoka Formation of Arkansas: American 

Association of Petroleum Geologists Bulletin, v. 37, p. 1935–1953.

Horner, G.J., and Craig, W.W., 1984, The Sylamore Sandstone of north-central Arkansas, 

with emphasis on the origin of its phosphate, in McFarland, J.D., III, ed., Contributions 

to the geology of Arkansas, v. 2: Arkansas Geological Commission, p. 51–85.

Hudson, M.R., 1998, Geologic map of parts of the Jasper, Hasty, Ponca, Gaither, and 

Harrison quadrangles in and adjacent to Buffalo National River, northwestern Arkansas: 

U.S. Geological Survey Open-File Report 98–116, scale 1:24,000. 

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dome of northern Arkansas: Deformation in a late Paleozoic foreland: Geology, v. 28, 

p. 511–514.

Hudson, M.R., Murray, K.E., and Pezzutti, D., 2001, Geologic map of the Jasper 

quadrangle, Newton and Boone Counties, Arkansas: U.S. Geological Survey Miscellaneous Field Studies Map MF-2356, scale 1:24,000.

Hudson, M.R., and Murray, K.E., 2003, Geologic map of the Ponca quadrangle, Newton, 

Boone, and Carroll Counties, Arkansas: U.S. Geological Survey Miscellaneous Field 

Studies Map MF-2412, scale 1:24,000.

Hudson, M.R., and Murray, K.E., 2004, Geologic map of the Hasty quadrangle, Newton 

and Boone Counties, Arkansas: U.S. Geological Survey Scientific Investigations Map 

2847, scale 1:24,000, http://pubs.usgs.gov/sim/2004/2847/. 

Hudson, M.R., Turner, K.J., and Repetski, J.E., 2006, Geologic map of the Western Grove 

Quadrangle, Northwestern Arkansas: U.S. Geological Survey Scientific Investigations 

Map 2921, 1:24,000 scale, http://pubs.usgs.gov/sim/2006/2921/.

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and Madison Counties, Arkansas: U.S. Geological Survey Scientific Investigations Map 

2991, 1:24,000 scale, http://pubs.usgs.gov/sim/2991/. 

Manger, W.L., and Sutherland, P.K., 1992, Analysis of sections presumed to be complete 

across the Mississippian-Pennsylvanian boundary, southern mid-continent, in Sutherland, P.K., and Manger, W.L., eds., Recent advances in middle Carboniferous 

biostratigraphy—A symposium: Oklahoma Geological Survey Circular 94, p. 69–79.

McFarland, J.D., III, 1988, The Paleozoic rocks of the Ponca region, Buffalo National River, 

Arkansas, in Hayward, O.T., ed., Centennial Field Trip Guide, v. 4: Geological Society 

of America, p. 207–210.

McKnight, E.T., 1935, Zinc and lead deposits of northern Arkansas: U.S. Geological Survey 

Bulletin 853, 311 p.

McKnight, E.T., and Fischer, R.P., 1970, Geology and ore deposits of the Picher field, 

Oklahoma and Kansas: U.S. Geological Survey Professional Paper 588, 165 p.

Purdue, A.H., and Miser, H.D., 1916, Descriptions of the Eureka Springs and Harrison 

quadrangles: U.S. Geological Survey Atlas, Folio 202, scale 1:125,000.

Suhm, R.A., 1974, Stratigraphy of Everton Formation (early Medial Ordovician), northern 

Arkansas: American Association of Petroleum Geologists Bulletin, v. 58, p. 685–707.

Sutherland, P.K., 1988, Late Mississippian and Pennsylvanian depositional history in the 

Arkoma basin area, Oklahoma and Arkansas: Geological Society of America Bulletin, v. 

100, p. 1787–1802.

Zachry, D.L., 1977, Stratigraphy of middle and upper Bloyd strata (Pennsylvanian, 

Morrowan), northwestern Arkansas, in Sutherland, P.K., and Manger, W.L., eds., 

Upper Chesterian-Morrowan stratigraphy and the Mississippian-Pennsylvanian boundary in northeastern Oklahoma and northwestern Arkansas: Oklahoma Geological 

Survey Guidebook 18, p. 61–66.

Qal

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ST. JOE FAULT

MILL CREEK GRABEN

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CONFEDERATE FAULT

U.S. GEOLOGICAL SURVEY

Version 1.0

U.S. NATIONAL PARK SERVICE

1 .5 0 1 KILOMETER

SCALE 1:24 000

CONTOUR INTERVAL 20 FEET

NATIONAL GEODETIC VERTICAL DATUM OF 1929

1 1/ 2 0 1 MILE MAGNETIC NORTH

6.5°

APPROXIMATE MEAN

DECLINATION, 1967 TRUE NORTH

Any use of trade names is for descriptive purposes only 

and does not imply endorsement by the U.S. Government

This map was produced on request, directly from 

digital files, on an electronic plotter

For sale by U.S. Geological Survey Information Services

Box 25286, Federal Center, Denver, CO 80225

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ArcInfo coverages and a PDF for this map are available at 

http://pubs.usgs.gov/sim/3074/

Suggested citation:

Hudson, M.R., and Turner, K.J., 2009, Geologic map of the

St. Joe quadrangle, Searcy and Marion Counties, Arkansas:

U.S. Geological Survey Scientific Investigations Map 3074,

scale 1:24,000.

QUADRANGLE LOCATION

ARKANSAS

Geology mapped by M.R. Hudson and K.J. Turner,

2005–2008

Digital map database prepared by Kenzie J. Turner

Editing and digital cartography by

Gayle M. Dumonceaux

Denver Publishing Service Center

Manuscript approved for publication March 20, 2009

Base from U.S. Geological Survey, 1967

Projection and 10,000-foot grid ticks: Arkansas

coodinate system, north zone

1000-meter Universal Transverse Mercator grid, zone 15

1927 North American Datum

GEOLOGIC MAP OF THE ST. JOE QUADRANGLE, SEARCY AND MARION COUNTIES, ARKANSAS

By

Mark R. Hudson and Kenzie J. Turner

2009

CONVERSION FACTORS

Multiply By To obtain

inches (in.) 2.54 centimeters (cm)

feet (ft) 0.3048 meters (m)

miles (mi) 1.609 kilometers (km)