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Home , Alleghanian orogeny, Brallier Formation, Huntersville Chert, Juniata Formation, Keyser Formation, Martinsburg Formation

VIRGINIA DIVISION OF AND MINERAL RESOURCES

PUBLICATION 178

GEOLOGY OF THE MONTEREY QUADRANGLE,

Gerald P. Wilkes

COMMONWEALTH OF VIRGINIA DEPARTMENT OF MINES, MINERAL AND ENERGY DIVISION OF GEOLOGY AND MINERAL RESOURCES David B. Spears, State Geologist

CHARLOTTESVILLE, VIRGINIA 2011 (Revised April 2013) FRONT COVER: Trimble Knob in winter with Monterey Mountain in background. This landform, south of Monterey, is the remnant of an ancient volcano. CONTENTS

Introduction...... 1

Stratigraphy…..…………………………………………………………………………...... 2 Paleozoic…………………………………...... ……………………...... ……2 ...... …………….....……………………………………………………2 Beekmantown Formation……………………………………….....………2 Middle Ordovician ...... 3 Lower member…………...…………………………………..……3 Middle member……...... ………………….……3 Upper member….…...... …………………….……3 Dolly Ridge Formation……………………………...... ………4 Reedsville Shale and Oswego ..……………………...... ……4 ………………………………………………..…..……4 ……………………………………………..……...... 5 …………………………………………………....…5 and Keefer Sandstone.………………....………..……5 McKenzie Formation…………………………………………...…….……5 Williamsport Sandstone…...... …...... ……….…….……6 and Tonoloway Limestone…………….…….……6 ………………………………………………………...... …7 …………………………………………………....……7 ...... ………………………....……8 Needmore Formation and Millboro Shale…………………………....……8 ...... 9 Mesozoic and Cenozoic…………...... …………………………...... …9 Igneous rocks………………………………………………….…...... …9 Surficial deposits………………………………………………...... …..10

Structural Geology...... 11 Regional Setting...... 11 Allgehany Plateaus province...... 11 Alleghany structural front...... 11 Valley and Ridge province...... 11 Hightown ...... 11 Monterey syncline...... 12 Bolar anticline...... 12 Jack Mountain anticline...... 13 Bear Mountain fault...... 13 Shenandoah Igneous Province...... 14

Economic Geology...... 14 Limestone and dolostone...... 14 Sandstone and ...... 15 Shale...... 16 Oil and Gas...... 16 Brucite...... 16 Non-polishing aggregate...... 16 Soda feldspar...... 16 Precious minerals...... 16

References cited...... 17

ILLUSTRATIONS

Plate 1. Geologic Map of the Monterey quadrangle, Virginia

Figures 1. Location of the Monterey quadrangle...... 1 2. Barren Rock on northern Jack Mountain...... 2 3. Hightown Valley looking west from Monterey Mountain...... 3 4. Sinkholes in the middle Ordovician rock unit...... 4 5. Devils Backbone seen from Bluegrass...... 5 6. Ripple marks in the Rose Hill...... 5 7. A minor fault in the Williamsport Sandstone along State Route 642...... 6 8. An unnamed sandstone bed in the Wills Creek Formation...... 7 9. Corriganville limestone outcrop along Strait Creek...... 8 10. The lowest part of the Ridgely Sandstone...... 8 11. Millboro Shale containing concretions...... 9 12. ...... 10 13. Landforms in the Hightown valley made from both alkalic and mafic rock...... 10 14. Volcanic Breccia outcrop...... 10 15. Talus below Barren Rock on northern Jack Mountain...... 11 16. Alleghany Structural Front in Pendleton County, ...... 12 17. View of Hightown Valley...... 12 18. View of Bolar Valley...... 13 19. Barren Rock on northern Jack Mountain...... 13 20. Rockbridge Stone Products #1 quarry...... 14 21. Abandoned limestone quarry east of Monterey...... 15 22. Residual borrow pit...... 15 23. Tuscarora talus at base of Devils Backbone...... 16 PUBLICATION 178 1

GEOLOGY OF THE MONTEREY QUADRANGLE, VIRGINIA

Gerald P. Wilkes

INTRODUCTION

The Monterey Quadrangle is located in Highland County, Virginia and Pendleton County, West Virginia (Figure 1). Bedrock in the quadrangle includes Ordovician, Silurian, and Devonian carbonate and clastic rocks. These rocks were folded and faulted during the Alleghanian Orogeny in the late Paleozoic. Multiple igneous events during the Mesozoic and Cenozoic intruded the Paleozoic rocks with dikes, sills and plugs. Masking most of the bedrock is a mantle of soils of Pleistocene and Holocene age. A variety of economic rock deposits can be found in the quadrangle and others possibly exist. Charles Butts (1933, 1940) offered the first comprehensive geologic map and stratigraphic synthesis of the Monterey area at a scale of 1:250,000. Rader and Wilkes (2001) produced a 1:100,000-scale geologic map, which refined Figure 1. Location of the Monterey quadrangle. Butts’ mapping. Additional geologic mapping was conducted in the Bluegrass Valley portion of A geographic oddity within the quadrangle the Monterey 7.5’ quadrangle by Parrott (1948) can lead to confusion when describing the geology. and Tarleton (1948). Kettren (1970) mapped in There are two Jack Mountains in the southeastern the upper reaches of the Strait Creek area, paying portion of the quadrangle, and although they are special attention to the many igneous bodies in a single physiographic mountain range, they are that vicinity. Tso and Surber (2003) mapped formed by two different geological structures: a portion of the Monterey quadrangle, also in the Bolar anticline and Jack Mountain anticline. the Strait Creek section of the quadrangle. A To differentiate the two mountains throughout Virginia Geological Field Conference (Tso and this report, the Jack Mountain that is crossed by others, 2003) and a Geological U.S. 250 east of Monterey will be referred to as Survey field guide (Southworth and Burton, “southern Jack Mountain”. The Jack Mountain 2004) have focused on the igneous rocks that that separates Doe Hill from the Monterey valley occur in the quadrangle. Mapping in adjacent will be referred to as “northern Jack Mountain.” quadrangles by Clough (1948), Ramsey (1950), In the course of this investigation, it became and McDowell and others (2000 and 2002) apparent that the landform locally known as were consulted in geologic interpretation of the Barren Rock on northern Jack Mountain has been Monterey quadrangle. erroneously shown on maps as Riven Rocks for PUBLICATION 178 2 at least the last 100 years. After extensive review, especially including the citizens of Highland County, the United States Board of Geographic The Monterey quadrangle contains Names has revised their files, and future maps Paleozoic clastic and carbonate sedimentary will read Barren Rock (Figure 2). rock and Mesozoic and Cenozoic . Much assistance and insight to the geology The oldest Paleozoic rock to outcrop is lower of the area was given to the author by Thomas Ordovician carbonate rock that is unconformably Gathright, Eugene Rader, Roy Sites, and Palmer overlain by middle Ordovician carbonates. Sweet of the Virginia Division of Geology The middle Ordovician carbonates gradually and Mineral Resources (DGMR), Barrie Wolf transition over several hundred feet into upper (United States Natural Resources Conservation Ordovician clastic rock. All Ordovician rock in Service) and Jon Tso (Radford University). Ron the Monterey quadrangle is limited in surface McDowell, Lee Avary, and Doug Patchen (West extent to the Bluegrass Valley. Above the Virginia Geologic and Economic Survey) also Ordovician, lower and middle Silurian clastic provided useful, field-oriented observations. Also rock includes resistant ledge-forming beds that helpful was Roger Moyer (Virginia Department hold up the crests of Lantz, most of Monterey, of Forestry), Rick Lambert, Connie Schwartz, and and both of the Jack mountains. Upper Silurian the staff at the Highland County courthouse. John clastic rock grades upward into a carbonate- Haynes (James Madison University) provided dominated package that rims Monterey valley additional edits that improved this report. Access and the Strait Creek area. Conformably above the to private land is valuable to field investigation Silurian is lower Devonian clastic and carbonate and the citizens of Highland County willingness rock that is unconformably overlain by middle to allow access to their properties made mapping Devonian clastic rock. These latter rocks are the this area a true pleasure. youngest Paleozoic bedrock in the quadrangle and are found in the Monterey valley, along the west face of Lantz Mountain and the east face of Alleghany Mountain. An unusual swarm of Mesozoic and Cenozoic igneous rock intrudes the Paleozoic rock and is known as the Shenandoah igneous province (McHone, 1988 and Vogt, 1991). These igneous rocks are the youngest rock in the quadrangle, and also the youngest igneous rocks on the North American east coast (Johnson and others, 1971). Pleistocene and Holocene residual and transported soil blanket the landscape, concealing much of the bedrock.

ORDOVICIAN

Beekmantown Formation (Ob)

Figure 2. Barren Rock on northern Jack Moun- Rock of the lower Ordovician Beekmantown tain, looking northeast from southern Jack Moun- Formation is dominantly light-gray, fine- tain. grained, thick-bedded dolostone. Also within PUBLICATION 178 3 the Beekmantown are thin (less than 2 feet Middle Ordovician limestone thick) light-gray, fine-grained limestone beds. Black chert is found throughout the exposed Immediately above the Knox portion of the formation as both nodules and and below the Dolly Ridge Formation are undulating beds. Unique to the Beekmantown three lithologically distinctive units of middle is a white, massive chert bed, about 15-feet Ordovician-age carbonate rock. Studies thick and found approximately 100 feet below elsewhere in Virginia and West Virginia in this the top of the formation. This chert bed, being part of the stratigraphic section have applied a resistant to erosion, holds up the unnamed hill variety of names to these units. In order to avoid in the central Bluegrass Valley (Figure 3). A confusion, this report refers to them simply number of well-formed, doubly terminated as lower, middle, and upper members. The quartz crystals have been found associated with following discussion distinguishes the units by the massive chert bed. Being highly susceptible their lithology, recognizing that each unit has to weathering, the Beekmantown forms a thick a unique paleodepositional history. Contacts soil profile and is conspicuous by its lack of between these units and the overlying Dolly natural outcrop. Contact of the Beekmantown Ridge Limestone are all graded over 50 to 100- with the overlying middle Ordovician limestone foot intervals. unit was not observed but is assumed to be unconformable (Knox Unconformity). Where Lower member seen in other locations, this unconformity may (Oml) have several feet of paleotopographic relief and display lag deposits of well-rounded dolostone The lower member consists of interbedded clasts. The Beekmantown is the oldest rock in limestone and dolostone that are medium-gray, the quadrangle, and only the uppermost few medium- to thin- wavy bedded and contain hundred feet are exposed. Good outcrops of the gypsum nodules, rip-ups, and rounded fine- Beekmantown are present along State Route 640 grained quartz sand grains. There is at least one in the Bluegrass Valley. thin gray shale bed included with this member. The lower member is approximately 100 feet thick and found on the lowest slopes of the Bluegrass Valley.

Middle member (Omm)

The middle member is medium- to dark-gray, micrograined to very-fine grained, thick-bedded limestone. It contains black chert as nodules and beds. The middle member is approximately 180 feet thick and is found on the lower slopes of the Bluegrass Valley.

Figure 3. Hightown Valley looking west from Upper member Monterey Mountain. The linear hill in the center (Omu) of the valley is held up by an erosionally-resis- tant chert bed in the Beekmantown Formation. The upper member is typically light-gray, wavy Lantz Mountain in the background. bedded, medium- to coarse-grained limestone with some light-gray micrite beds. Karst PUBLICATION 178 4 topography in the form of sinkholes, caves and pinnacle weathering is common in this unit (Figure 4). The upper member is about 50 feet thick and exposed on the lower slopes of the Bluegrass Valley at about the break in slope.

Dolly Ridge Formation (Odr)

This upper Ordovician formation consists of limestone that is medium-gray, knobby- and wavy-bedded, aphanic, and fossiliferous (including worm tube fillings). It is about 300 feet thick, and equivalent to the lower of the eastern outcrop Figure 4. Sinkholes, a type of karst topogra- belts and the in West Virginia. phy, are common in the middle Ordovician rock The Dolly Ridge has a gradational contact with unit. These geomorphic features are a sign that the overlying Reedsville Shale and is placed at the limestone bedrock is being hollowed out by the top of the last limestone of the Dolly Ridge. groundwater and forming caves. When the roof of the cave collapses, the surface expression is a Reedsville Shale and Oswego Sandstone sinkhole. (Oro)

The Reedsville Shale is a sequence of interbedded greenish-gray to grayish-brown mudstone and shale with thin interbeds of to erosion relative to the surrounding rock, the fossiliferous sandstone. Near the top of the Oswego forms a subtle break in slope on the west Reedsville is a prominent sandstone that is a flank of Monterey Mountain. regional marker bed, the Orthorynchula zone of Butts (1940). The Reedsville is equivalent Juniata Formation to the upper Martinsburg Formation of the eastern (Oj) outcrop belts and has a gradational contact with the overlying Juniata Formation. The contact Interbedded yellowish-brown to red is placed at the first red bed of the Juniata. The sandstone, and olive-gray and red shale and Reedsville is well exposed along U. S. 250 on the mudstone typify the Juniata Formation. At the west flank of Monterey Mountain where Chen top of the Juniata in the Monterey quadrangle (1981) measured 1215 feet of section. are several blue-gray quartzarenite beds, up to 5 On the Monterey quadrangle the Oswego feet thick, interbedded with red mudstone. These Sandstone is too thin to consistently map resistant rocks cap Monterey Mountain where U. at 1:24,000-scale and is included with the S. 250 crosses the crest. The Juniata is found on Reedsville map unit. The Oswego Sandstone the east flank of Lantz Mountain, the west flank lies above the Orthorhynchula zone and below of northern Jack Mountain and on the west flank the overlying Juniata Formation and is brown, of Monterey Mountain where it is approximately medium- to coarse-grained, thick-bedded, iron- 725 feet thick (Butts, 1940). Contact of the speckled sandstone with partings of green and Juniata with the overlying Tuscarora Formation red shale. Both upper and lower contacts of the is unconformable and placed at the base of the Oswego are sharp. Because of its resistance first orthoquartzite of the Tuscarora. PUBLICATION 178 5

SILURIAN Rose Hill Formation is sharp and placed at the top of the last quartzarenite of the Tuscarora. Tuscarora Sandstone (Stu) Rose Hill Formation and Keefer Sandstone (Srh) The Tuscarora Formation is sandstone and orthoquartzite that is white to light-gray, medium- The distinctive lithology of the Rose Hill to coarse-grained, and thin- to very thick-bedded. Formation is dark-maroon, thick-bedded, Thin beds of quartz-pebble conglomerate indurated, hematitic sandstone that may have a occur in the lower half of the formation. The metallic sheen. This sandstone is bounded above Tuscarora displays cross-bedding, clay rip-ups and below by greenish-gray to red shale with and the trace Arthrophycus alleghaniensis thin gray sandstone interbeds, some of which and Skolithos. Comprised of strongly welded have abundant fossils. Ripple marks quartzite and sandstone, the Tuscarora is the are common on the sandstone beds (Figure 6). most resistant to weathering of any of the The Rose Hill is 200 to 250 feet thick and well Paleozoic rocks in the Monterey area. As a exposed on the east flank of Monterey Mountain result, it plays a prominent role in the shaping above the antenna farm along U. S. 250. Contact of the local topography. The Tuscarora caps of the Rose Hill is gradational with the overlying Lantz Mountain and its outcrop can be easily McKenzie Formation and placed at the last red viewed from the Bluegrass Valley. Beds of the bed of the Rose Hill. The Keefer Sandstone, Tuscarora hold up most of Monterey Mountain’s which is five to ten feet thick in the Monterey crest. The Devils Backbone is Tuscarora area, occurs between the Rose Hill and McKenzie Sandstone and can be observed from several formations and was mapped with the Rose Hill vantages north of Monterey and the Bluegrass Formation. Valley (Figure 5). Both of the Jack Mountains, prominent topographic features in the area, are McKenzie Formation likewise capped by the Tuscarora Sandstone. To (Smc) the south of the quadrangle, excellent Tuscarora exposures within the Jack Mountain anticline The McKenzie Formation consists of gray, are easily seen in Crab Run between Monterey medium-bedded, fine- to medium-grained and McDowell. This formation is 84 feet thick sandstone that is calcareously cemented, at Devils Backbone. Contact with the overlying

Figure 5. Exemplifying its resistance to weather- Figure 6. These well-preserved ripple marks are ing, the Tuscarora Sandstone is the Devils Back- within the Rose Hill Formation on the east flank bone, as seen in this view from Blue Grass (pho- of northern Jack Mountain. Flamingo for scale. tograph by David Spears). PUBLICATION 178 6 cross-bedded, and may display ripple marks. Wills Creek Formation and Tonoloway The sandstone is interbedded with knobby- Limestone weathering, abundantly fossiliferous (especially (Stw) ostracoda) limestone. The McKenzie is highly susceptible to weathering and is poorly exposed in The Wills Creek and Tonoloway erode natural outcrop within the quadrangle. However, easily, are poorly exposed, and have a gradational there is an excellent exposure in the roadcut contact with one another. They are mapped as for State Route 642 west of Forks of Waters, one unit. where it is approximately 165 feet thick (Butts, 1940). Contact with the overlying Williamsport Wills Creek Formation Sandstone is unconformable. The Wills Creek Formation consists of Williamsport Sandstone gray-green weathering calcareous shale and (Sw) mudstone that is thin- to medium-bedded, and interbedded with light-gray, thin-bedded, fine- The Williamsport Sandstone is light-gray grained, argillaceous limestone. The limestone to white, thick-bedded, fine- to medium-grained occasionally displays mudcracks, ripplemarks, quartzarenite, welded by silica cement. It is and salt crystal casts. Another sandstone, often cross-bedded and contains fucoids (Figure found about 60 to 90 feet below the base of the 7). The Williamsport is an important marker bed Tonoloway, is light tan, fine- to medium-grained, in the Monterey quadrangle, readily recognizable calcareously cemented and 5 feet thick. It is because of its resistance to weathering in natural in sharp contact with underlying medium-gray, outcrop. In the Strait Creek area, the Williamsport coarse-grained, petroliferous limestone (Figure is 31 feet thick. The Williamsport is conformable 8). Contact of the Wills Creek with the overlying with the overlying Wills Creek Formation. Tonoloway Limestone is gradational. Woodward On the geologic map, the line separating the (1941) measured 213 feet of Wills Creek along McKenzie and Wills Creek formations represents the South Branch of the near the outcrop trace of the Williamsport. Forks of Waters.

Tonoloway Limestone

The is divided into three units. The lower and upper units are characterized as dark-gray to black, thin-bedded, thinly- laminated, argillaceous limestone that weathers to tan channery soil. Sand grains have been noted in these units. The middle unit is an aggregate of irregularly bedded limestone, and knobby-weathering blue limestone. This unit is highly fossiliferous, particularly with Stromatopora. Butts (1940) measured 450 feet of Tonoloway near Forks of Waters. The Figure 7. A minor thrust fault in an otherwise contact with the overlying Helderberg Group is complete section of Williamsport sandstone conformable. along State Route 642. The Williamsport sepa- rates the Wills Creek Formation, above, from the McKenzie Formation, below. PUBLICATION 178 7

member, Byers Island, is medium-gray, coarse- grained, arenaceous, thin- to thick-bedded limestone. This member is 75 feet thick east of Monterey (Swartz, 1929). The Byers Island contact with the overlying Big Mountain Shale is conformable. The Big Mountain Shale is the middle member of the Keyser. Although difficult to find as fresh outcrop, it weathers to a light-gray to yellowish channery soil. The Big Mountain Shale is 32 feet thick on the east Figure 8. An unnamed sandstone bed in the Wills slope of Monterey Mountain and is equivalent Creek Formation is easily seen on the north flank to the Clifton Forge Sandstone in Bath County. of Ginseng Mountain. Contact with the overlying Jersey Shore member of the Keyser is conformable. The upper Jersey Shore member is medium-gray, medium-grained, thick-bedded limestone. It is 125 feet thick east of Monterey (Swartz, 1929). Contact with the upper New Creek Limestone is conformable. The Silurian-Devonian boundary is located within the Helderberg Group Keyser (Denkler and Harris, 1988). The Keyser (DSh) Formation is well exposed in outcrops along the Strait Creek road. Formations within this group have distinct lithologies and are laterally persistent. However, New Creek Limestone individual formational thicknesses preclude depicting them at the maps 1:24,000-scale. All The New Creek is light-gray to pink, rocks above the Tonoloway Limestone and coarse-grained, thick-bedded limestone. It is below the Ridgeley Sandstone define this map identifiable by the abundance of gray and pink unit. This map unit includes, from oldest to segments and emits a petroliferous odor youngest, the , New Creek from fresh outcrop. The New Creek Limestone Limestone, Corriganville Limestone, and the is conformable with the overlying Corriganville Licking Creek Limestone. Chert beds within Limestone and is 20 to 60 feet thick. It is well the Helderberg Goup provide an armoring effect exposed in outcrops along Strait Creek. upon the landscape thus forming the Rich Hills, Seybert Hills, Miracle Ridge, The Alley Cup, Corriganville and Licking Creek Ginseng Mountain and other unnamed hills in the Monterey valley. The Corriganville and Licking Creek Limestones were mapped together. The Corriganville limestone is about 35 feet thick DEVONIAN with characteristic lenses and nodules of white to gray chert (Figure 9). The Licking Creek Keyser Formation Limestone is the uppermost formation of the Helderberg Group. Head (1972) divided the The Keyser Formation was divided into Licking Creek into two members, both found three members by Head (1972) and all are in the Monterey area. The lower Cherry Run recognizable within the quadrangle. The lowest member is medium-gray, fine-grained, thick- bedded limestone recognizable for the abundance PUBLICATION 178 8 of black chert along bedding planes. The Cherry Millboro Shale and Needmore Formation Run is conformable with the overlying Little (Dmn) Cove member. The upper Little Cove member is medium gray, arenaceous, thick-bedded Because of poor exposure, the Millboro limestone. The Little Cove is conformable with Shale and the Needmore Formation could not the overlying Ridgeley Sandstone and is 50 to be consistently differentiated and therefore were 130 feet thick. mapped as one unit. On the Monterey quadrangle this map unit underlies valley bottoms because of Ridgeley Sandstone its susceptibility to weathering. (Dr) Needmore Formation The Ridgeley Sandstone is tan to light-gray, medium- to coarse-grained, calcareous cemented, The Needmore Formation is medium- to light- thick-bedded sandstone. It is cross-bedded, olive-gray shale with minor amounts of limestone fossiliferous (abundant diagnostic Spiriferid and thin bentonite beds near the top (Tioga ash brachipods) and can be highly ferruginous. In beds). , , arthropods, places, the Ridgeley has thin zones of well- including , and bryozoans are common rounded quartz pebble “jelly bean” conglomerate. fossils. Contact with the overlying Millboro The Ridgeley is approximately 100 feet thick Shale is conformable. The Needmore is poorly within the quadrangle and unconformable with exposed in the quadrangle, but it is 150 feet thick the overlying . Included with the on the east flank of Bullpasture Mountain to the Ridgeley map unit is the overlying Huntersville south in Bath County (Butts, 1940). Chert which has a graded contact with the Ridgeley. Because of the flat-lying nature of this Millboro Shale formation north of Monterey, there are several localities of very well exposed Ridgeley such as The Millboro Shale is black, fissile shale along State Route 632. containing thin bentonite interbeds and may

Figure 9. Corriganville limestone outcrop along Figure 10. In this outcrop along Strait Creek, the Strait Creek. Gray nodular chert in this weath- lowest part of the Ridgely Sandstone contains ered exposure clearly delineates bedding planes. chert beds that may be equivalent to the Shriver chert. PUBLICATION 178 9 contain concretions (Figure 11). Black, thin- to beds occur throughout the Brallier (Charles Ver thick-bedded microcrystalline limestone beds Straeten, State Museum, personal may be found near the base of the unit (Purcell communication). Only the basal few hundred equivalent). The Millboro is a structurally feet of the Brallier occurs in the quadrangle incompetent unit and has been subjected to where it is exposed on the east flank of Alleghany considerable deformation. Slickensides, Mountain. secondary mineralization, and small-scale faults are observed in most outcrops. Where observable, contact with the overlying Brallier Formation is MESOZOIC AND CENOZOIC gradational and placed at the uppermost black shale of the Millboro. There are lithologic Igneous Rocks affinities of the Manhantango Shale within the Millboro suggesting a distal facies relationship Igneous rocks within the Monterey between the two units. Because of the intensive quadrangle occur as mafic and felsic dikes and folding and faulting of the Millboro the exact sills, and as volcanic breccia plugs. Dikes and thickness is difficult to determine, however Butts sills are apparently related to regional jointing (1940) measured about 1000 feet in southern and bedding whereas plugs seem to be randomly Highland County on the east flank of Bullpasture dispersed. The formation of these bodies is Mountain. discussed by several authors including Tso and others (2004) and Rader and others (1986). Brallier Formation Mafic rocks are dark gray to black and range from (Db) aphanitic to porphyritic in texture (Figure 12). Phenocrysts include plagioclase, clinopyroxene, The Brallier Formation consists of olivine and biotite. Matrix material includes green, brown, and gray, platy, micaceous shale abundant thin laths of plagioclase, magnetite and interbedded with numerous gray, very fine- clinopyroxene. Amygdules may be present and grained, thinly-bedded sandstone and siltstone filled with zeolite minerals, and quartz. beds that are sparsely fossiliferous. Thin bentonite Xenoliths of country rock are common. Felsic rocks are white to medium-gray and weather to a buff color. The most abundant mineral in all felsic rock is plagioclase. Most felsic rocks are porphyritic with phenocrysts composed mostly of plagioclase, biotite and hornblende. Amygdules may occur in felsic rock, but less commonly than in the mafic rocks. Xenoliths of may be present. The third type of igneous rock is volcanic breccia (Figure 13 and 14). It is dark-gray to black and contains abundant xenoliths of igneous and sedimentary rock and crystals of minerals such as plagioclase, olivine, clinopyroxene, hornblende and biotite. Xenoliths range in length from tenths of an inch to a few feet. Breccia often forms a more-or-less circular Figure 11. Millboro Shale containing concre- map pattern that is interpreted to be eroded cross- tions. These concretions may be septarian with sectional view of a diatreme pipe. barite or calcite fillings. A comprehensive publication of available chemistry of these intrusives has been published PUBLICATION 178 10

Surficial Deposits

Soil on the Monterey quadrangle is either residual or transported. Residual soil is derived from the parent bedrock and directly reflects the properties of that rock. In carbonate terrain (Beekmantown Formation, middle Ordovician limestones, Dolly Ridge Formation, Wills Creek Formation, Tonoloway Formation, and most of the Helderburg Group rocks), the soil tends to be red, sticky, and have low permeability. Residual soil derived from clastic rock (Reedsville Shale, Juniata Formation, Tuscarora Formation, Rose Figure 12. Basalt intrusive rock in the Hightown Hill Formation, McKenzie Formation, Ridgeley Valley. It typically weathers with a rough, gnarly Sandstone, Millboro Shale, and the Brallier texture. Formation) is generally lighter colored and less plastic than its carbonate counterpart. by McDowell (2001). Geophysical studies of the Transported soil exists as alluvial and intrusions are reported by Ressetar and Martin colluvial deposits. Alluvial soils are associated (1980). Age dating has been published by Zartman with actively running streams. They include and others (1967). An interesting study of the terrace deposits that are remnants of prior influence of igneous bodies exposed in caves stream migration. Colluvial deposits cover and their relationship to higher concentrations most mountain slopes. In hollows and below of radon was done by Whitelaw and Hevener rock outcropping, colluvium takes the form of (1994). boulder trains and talus that have formed from a combination of gravity, freeze-thaw action and catastrophic rain events (Figure 15). At the base

Figure 14. A closer look at a volcanic breccia in Figure 13. These landforms in the Hightown val- the lower Strait Creek area. Within the breccia ley are underlain by both alkalic and mafic intru- are variable sized clasts of Paleozoic sedimen- sive rocks. tary rock fragments as well as igneous rock frag- ments. PUBLICATION 178 11 of mountain slopes, colluvium coalesces into fans near valley floors. A survey of both residual and transported soils is currently being conducted in the Monterey quadrangle by the United States Natural Resource Conservation Service. It will be published as part of the Highland County soil survey.

STRUCTURAL GEOLOGY

Figure 15. Talus below Barren Rock on northern REGIONAL SETTING Jack Mountain. These deposits occur below Tus- carora ledges on Lantz, Monterey, and the Jack Three geologic provinces are represented mountains. on the Monterey quadrangle. These are the Alleghany Plateaus, Valley and Ridge and the Shenandoah Igneous provinces. In the extreme northwest corner of the quadrangle is the Shenandoah Igneous Province Monterey quadrangle is the Allegheny Plateaus and is represented by a final event of post- physiographic province. This area is composed Paleozoic extensional forces which allowed of Devonian and younger Paleozoic rock that is intrusion of igneous rock into the surrounding relatively unaffected by tectonism. bedrock. The rest of the quadrangle is located in the central Appalachian Valley and Ridge province. This area contains Devonian and ALLEGHANY PLATEAUS PROVINCE older Paleozoic rocks that have been folded and faulted by compressional forces during the Alleghany structural front Alleghanian Orogeny. The structural style of Valley and Ridge rocks in the Monterey area is Straight Fork is the demarcation between further influenced by late-Paleozoic deformation the Appalachian Plateaus to the west and the formed by transverse faulting of basement Valley and Ridge to the east. The regional rock. As examples, Kulander and Dean (1978) geologic and topographic feature formed west of recognized a northwest-trending structure in the creek is termed the Alleghany structural front Highland County that aligns with discrete blocks (Figure 16). Rocks of the Plateaus region are of the Alleghany Plateaus province. Pone and gently folded and have been minimally displaced others (1985) ascribe a strike-normal basement by faults. Only a small portion of the Plateaus structure to what they call the Highland County region is on the Monterey quadrangle, where it is lateral ramp. Southworth and others (1993) refer represented by the Devonian Brallier Formation. to a cross-strike basement fault and its influence on emplacement of post-Paleozoic igneous VALLEY AND RIDGE PROVINCE rocks. Marple and Talwani (2004) further define this cross-strike structure as the Shenandoah Hightown anticline fault, a strike-slip basement fault formed from the African cratons’ impact on North America The Hightown anticline is the westernmost during the Alleghanian Orogeny. structure of the Appalachian Valley and Ridge The third geologic province in the province in the quadrangle (Figure 17). To the PUBLICATION 178 12

part of the quadrangle. This geometry allows for the unusual amount of exposure of Millboro, Ridgely and Helderburg rock north of Monterey. North of the quadrangle, the Monterey syncline becomes incorporated into the Middle Mountain syncline of Grant and Pendleton counties, West Virginia. In the southern part of the quadrangle the syncline becomes asymmetric with the east limb steeper than the west limb. To the south of the quadrangle, the Monterey syncline can be traced through Bath County and looses surface expression in Alleghany County.

Figure 16. Looking west at the Alleghany Struc- Bolar anticline tural Front in Pendleton County, West Virginia. This prominent feature separates the Alleghany Named from the Bolar community on the Plateaus region from the Valley and Ridge prov- Bath-Highland county line, the Bolar anticline is ince. best seen to the south of the Monterey quadrangle in Big Valley where Ordovician- and Silurian- aged rocks reveal an asymmetric, west-verging anticline (Figure 18 and 21). On the Monterey north in West Virginia, the Hightown anticline Quadrangle, the Bolar anticline forms southern is known as the anticline, and Jack Mountain. As in the Bolar Valley, the anticline even further north, in , the same has a steep west limb, nearly horizontal crest and structure is the Nittany anticline (Perry, 1979). a gentle east limb. This box fold is consistent in To the south of Highland County the Hightown geometry with many other in western anticline becomes bifurcated into shorter Virginia. As the Bolar anticline plunges north, amplitude anticlines, most notably the Warm Springs anticline, and finally looses expression at the surface in Alleghany County, Virginia. On the Monterey quadrangle the western limb of the anticline is sharply overturned and has been subjected to forelimb shear thrusts. These later faults account for the exaggerated thickness of Ordovician shale on the west flank of the Bluegrass Valley. Strike-normal faults having a few feet of apparent displacement were noted in some rock outcrop within the structure. The Hightown anticline plunges north toward Snowy Mountain in West Virginia (McDowell and others, 2002).

Monterey syncline Figure 17. View of Hightown Valley, looking east from Monterey Mountain. The road seen The Monterey syncline is a gently in this view is U.S. 250, which is located on the southwestward plunging structure that has drainage divide between the Potomac River (to symmetrical gently-dipping limbs in the northern the right) and the James River (to the left). PUBLICATION 178 13

West Virginia (Figure 19). To the northeast of the Monterey quadrangle, the Jack Mountain anticline plunges and becomes assimilated into a series of anticlines and synclines on the Doe Hill quadrangle and into West Virginia. To the southwest, it becomes part of the east limb of the Bolar anticline. There is a physiographic offset of the Jack Mountain anticline with the regional structural grain. The implication of this observation is not fully understood but may have a relationship with basement structural Figure 18. Bolar Valley looking south from complexities. Sounding Knob. This anticlinal form enters the Monterey quadrangle as southern Jack Mountain. Bear Mountain Fault

The Bear Mountain fault is a southeast- dipping thrust fault with a maximum displacement of a few hundred feet. Its surface trace is it makes way to the gently folded Monterey approximately five miles in length with one end syncline on its west flank, while its east flank on Bear Mountain to the south of the Monterey becomes part of the Jack Mountain anticline. quadrangle and the other end on the Doe Hill quadrangle. Jack Mountain anticline SHENANDOAH IGNEOUS PROVINCE Only a part of the Jack Mountain anticline occurs within the Monterey quadrangle. The exposed portion is part of a larger geologic structure that is an anticline that has been broken by southeast-dippng thrust faults and minor back thrusts. Maximum throw on the faults is a few hundred feet as indicated by the Juniata thrust over the Rose Hill near the middle of the structure along the Jack Mountain Road. Several folds within this belt accommodate the displacement caused by faulting. For example, the core of the anticline can be seen on the Jack Mountain Road where Juniata redbeds have been folded into an anticline. This anticlinal structure of the Juniata Figure 19. Barren Rock on northern Jack Moun- is interrupted and exaggerated with several tain looking north from Wolf Rock (foreground). intraformational faults that reflect the nature the On the left, the outcrop of Tuscarora (Barren nearby, larger-displacement Jacks Fault. This Rock proper) is massive quartzite breccia and fault derives its name from the fact that it traverses identifies Jacks Fault. This fractured rock gives both northern and southern Jack Mountain. This rise to the large skree slope below the outcrop fault is best represented at Barren Rock where (see Figure 15). The outcrop of Tuscarora to the the Tuscarora Formation has been faulted right is the hanging wall exposure of the nearly against itself, in much the same way as at Seneca vertical Jacks Fault. Rocks and in Pendleton County, PUBLICATION 178 14

of the North American craton, one transecting During the Mesozoic, mafic and alkalic Highland County. Marple and Talwani bodies were intruded into the rock of the , (2004) further explored the existence of a pre- Blue Ridge and the Valley and Ridge provinces. Alleghanian northwest-trending basement fault In the , dikes, sills, plugs and volcanic (Shenandoah fault) reactivated during Mesozoic breccias were intruded through the Paleozoic to Cenozoic rifting. An age date of one Highland rocks of the Valley and Ridge. These later County igneous body is coincidental with timing intrusive rocks are unique to western Virginia and of the of the Chesapeake Bay impact crater eastern West Virginia. The entire suite of igneous (Diecchio, 2003). Key to all these theories is rock is referred to as the Shenandoah igneous a pre-existing structural weakness in basement province (McHone, 1988 and Vogt, 1991) and rock that allowed conduit for deep-seated magma is unique in that they are the youngest igneous to inject Paleozoic rock during the Mesozoic and rock in eastern North America (Johnson and again in the Cenozoic. others, 1971). Although evidence of localized metamorphism occurs, there is generally little wall rock alteration, which suggests a rapid, dry ECONOMIC GEOLOGY injection of the igneous rock (Sweet, 1996 and Tso and others, 2003). A mechanism for emplacement of these LIMESTONE AND DOLOSTONE intrusive bodies has not been completely resolved. Southworth and others (1993) Crushed limestone is currently being proposed extensional reactivation of basement produced from Rockbridge Stone Products, Inc. fracture zones with orientation of injection #1 Mine 1.5 miles north of Monterey (Figure 20). related to change in the regional stress field from The quarry is located on the west flank of Miracle the to the Eocene. Pone (1985) suggests Ridge and is working a fine section of upper structural lateral ramps along the east margin Tonoloway through upper Keyser formations. In the highwall and elsewhere on the property are mafic dikes and sills. In 2008, the quarry produced 79,334 tons, primarily for roadstone. The potential for other industrial minerals such as agricultural lime and non-polishing aggregate have not been investigated. Four abandoned quarries are located on the Monterey quadrangle. The Virginia Department of Highways operated a quarry on the east side of state route 640. It supplied stone to upgrade US 250. Beekmantown Formation rocks, the axial hinge of the Hightown anticline, and several igneous dikes and sills are well exposed in the quarry. A quarry east of State Road 637 was operated by Salem Stone Corporation and later Figure 20. Rockbridge Stone Products #1 Quar- by State Contracting and Stone Company from ry. This is the only active quarry in the quad- 1974 to 1979 in middle Ordovician limestone. rangle and provides crushed stone from the Hel- A third abandoned quarry east of Monterey at the derberg Group for several uses. This quarry was south flank of Rich Hill produced aggregate from developed in the 1990’s and has remained active Helderberg limestone. It was operated by the ever since. Virginia Department of Highways (Figure 21). PUBLICATION 178 15

A small abandoned quarry is located along State Route 629 in the Licking Creek Limestone. A quarry near New Hampden produced dimension stone from middle Ordovician limestone. Older buildings in the area, including the mill in New Hampden, used this stone for foundations. Several small farm pits have extracted residual chert derived from the Helderberg Group in the Monterey Valley (Figure 22). These unique deposits make excellent ballast for farm roads and fill. They appear to be pod-like deposits and Figure 22. This residual chert borrow pit pro- their extent is unknown. vides outstanding base material on local farm Giannini and Hostettler (1994) sampled roads. 62 limestone and dolostone outcrops in the Ordovician and Devonian carbonate rocks in the Hightown and Monterey valleys and analysed SANDSTONE AND QUARTZITE them for major-, minor-, and trace-elements, chlorine content and reflectance. Several of Sandstone and quartzite are used to make these analyses reveal uses suitable for aggregate, glass, as a metallurgical flux, in semiconductors, high-purity limestone for agricultural lime, water and in optical applications. In the Monterey purification, as a filler-extender in paint, paper, quadrangle, Sweet (1981) sampled and analyzed plastic and rubber products, use in coal-fired 25 sandstone and quartzite outcrops of the flue-gas scrubbers, and as a flux stone in the Tuscarora and Ridgeley for high- metallurgical industry. silica resources. One sample of Tuscarora from the Devils Backbone contained 98.6% SiO2 (Sweet, 1981). Lowrey (1954) reports 99.6% SiO2 from another sample of the Tuscarora Sandstone on Monterey Mountain. The Tuscarora Sandstone, Williamsport Sandstone and the ferruginous portion of the Rose Hill Formation may be a source for non-polishing aggregate within the quadrangle. West of Forks of Waters, the Tuscarora Sandstone is utilized as dimension stone. It is picked from the talus slope of Devils Backbone (Figure 23) and packaged in bundles for transport. The hematitic Rose Hill sandstone was an important iron ore source rock farther south in Alleghany and Craig counties. It was prospected for in the 1800’s in Highland County, but not deemed economic for mining at that time. There are unsubstantiated reports of historical glass manufacture south of Figure 21. Abandoned limestone quarry east of the Monterey quadrangle near Mustoe that, if Monterey. The dip of the beds displays the steep credible, probably utilized Ridgeley Sandstone west limb of the Bolar anticline. as the source material. PUBLICATION 178 16

STRUCTURAL CLAY PRODUCTS

Two exposures of shale were tested in the Monterey quadrangle for structural clay potential (Calver and others, 1964). Analyses of one sample from the Millboro Shale and one from the McKenzie Formation show a potential for use as brick. There may also be potential for structural clay products from the Brallier Formation and the Big Mountain Shale. These units have not yet been tested. Figure 23. Tuscarora talus at the base of Devils Backbone is used as dimension stone for founda- OIL AND GAS tions, walls and patio stone.

Three test holes were drilled within 50 miles of the Monterey quadrangle. These were all stratigraphic test holes that indicate the presence the Tuscarora Sandstone, Rose Hill Formation, of a lower decollement surface that may contain and mafic igneous rock may be suitable for this targets for oil or gas below that level (Perry, commodity. 1964). Recent developments in gas production from the Devonian Marcellus Shale elsewhere in the Appalachian Basin present an unknown SODA FELDSPAR potential for this target in the Monterey area. Albite-bearing dikes may contain enough salable-grade albite (soda) feldspar through BRUCITE simple processing methods (Garner, 1956). However, the transportation costs coupled with Brucite is used in the textile industry as the relatively small resource of ore available a decaustic agent to neutralize dyes, in paint and currently preclude development. in the making of PVC pipe. On the Monterey quadrangle, brucite is formed from the alteration of dolostone from igneous injection. The PRECIOUS MINERALS Virginia Division of Mineral Resources studied one locality for brucite and found that because Several alluvial diamonds have been of the limited extent of wall rock alteration in found in West Virginia and Virginia, but the the Highland intrusives, the economic potential source rocks have not been discovered. For at the site was unfavorable (Giannini and others, example, in 1928 the “Punch” Jones Diamond 1987 and Good, 1992). Several other sites exist was found to the west of the quadrangle at Rich but have not been publically investigated. Creek near Peterstown, West Virginia (Sweet, 1996). It weighed 34.48 carats and was the largest diamond found in North America at the time. If NON-POLISHING AGGREGATE native, there is a probability that this and the other finds have their source from intrusive rocks There are formations in the quadrangle that similar to those on the Monterey quadrangle. may have potential as non-polishing aggregate. Although testing has not been done, units such as PUBLICATION 178 17

REFERENCES CITED Garner, T. E., Jr., 1956, The igneous rocks of Pendleton County, West Virginia: West Butts, C., 1933, Geologic map of the Appalachian Virginia Geological and Economic Survey Valley of Virginia: Virginia Geological Report of Investigations 12, 31p. Survey Bulletin 42, 1:250,000-scale map. Giannini, W. F., Mitchell, R. S. and Mann, R. ______, 1940, Geology of the Appalachian W., 1987, Brucite from Highland County, Valley in Virginia: Virginia Geological Virginia: Virginia Division of Mineral Survey Bulletin 52, Part 1, 568 p. Resources Virginia Minerals v. 33, n. 1, p. 11. Calver, J. L., Smith, C. E. and Le Van, D. C., 1964, Analyses of clay, shale and related ______and Hostettler, K. K., 1994, materials- west central counties: Virginia Analyses of carbonate rocks- northwestern Division of Mineral Resources Mineral Virginia (Elkins-Staunton 0.5 x 1 Resources Report 5, 230 p. quadrangle): Virginia Division of Mineral Resources Publication 135, 160p. Chen, Ping-fan, 1981, Lower Paleozoic stratigraphy, tectonics, paleogeography, Good, R. S., 1992, Brucite marble occurrences and oil/gas possibilities in the central along Ordovician Beekmantown dolomite Appalachians (West Virginia and adjacent and Eocene basalt and andesite dike contacts, states), Part 2: measured sections: West Highland County, Virginia: in Sweet, P. C. Virginia Geological and Economic Survey (ed), 1992, Proceedings, 26th Forum on the Report of Investigation No. RI-26-2. Geology of Industrial Minerals: Virginia Division of Mineral Resources Publication Clough, W. A., 1948, Geology of the northern 119, pp. 143-151. portion of the Bolar Valley Anticline, Highland County, Virginia: University of Head, J. W., 1972, Upper Silurian- lower Virginia Masters thesis, p. (mic 4, n 2) Devonian stratigraphy and nomenclature in the central Appalachians: in Stratigraphy, Denkler, K. E. and Harris, A. G., 1988, - sedimentology, and structure of Silurian and based determination of the Silurian- Devonian rocks along the Devonian boundary in the Valley and Ridge in Bedford County, Pennsylvania, Allegheny province, north and central Appalachians: County, , and Mineral and Grant U. S. Geological Survey Bulletin 1837, p. counties, West Virginia: Pennsylvania B1-B13. Geological Survey Field Conference Guidebook, n. 37, p. 96-103. Diecchio, R. J., 2003, Relationships between geologic features in Highland County and Johnson, R. W., Milton, C. and Dennison, J. the Chesapeake impact structure: in Tso M., 1971, Field trip to the igneous rocks et.al, 2003, Middle Eocene igneous rocks in of Augusta, Rockingham, Highland, and the Valley and Ridge of Virginia and West Bath counties, Virginia: Virginia Division Virginia: 33rd annual Virginia Geologic of Mineral Resources Information Circular Field Conference, p. 29-31. 16, 68 p. PUBLICATION 178 18

Kettren, L. P., Jr., 1970, Relationship of igneous Publication OF-0101, 1:24,000-scale map intrusions to geologic structures in Highland and cross-sections. County, Virginia: Virginia Polytecnic Institute Masters thesis, 48 p. McHone, J. G., 1988, Tectonic and paleostress patterns of Mesozoic intrusions in eastern Kulander, B. R. and Dean, S. L., 1978, Gravity, North America: in Manspeizer, W. (ed) magnetics and structure, Alleghany Triassic-Jurassic rifting; continental breakup Plateau/western Valley and Ridge in West and the origin of the and Virginia and adjacent states: West Virginia passive margins, part B: Developments in Geological and Economic Survey Report of Geotectonics 22: Elsevier, p. 607-620. Investigations RI-27, 91 p. Mitra, S., 2002, Fold-accommodation faults: Lowry, W. D., 1954, Silica sand resources of American Association of Petroleum western Virginia: Virginia Polytechnical Geologists Bulletin, v. 86, n. 4, pp. 671- Institute and State University Bulletin, v. 693. 47, n. 12 (Engineering Experiment Station Series No. 96), 62 p. Parrott, E. W., 1948, Geology of the northern portion of the Hightown Anticline, Marple, R. and Talwani, P., 2004, Proposed Monterey quadrangle, Highland County, Shenandoah fault and East Coast-Stafford Virginia: M. S. thesis, University of Virginia, fault system and their implications for Charlottesville, Virginia, 99 p. Eastern U. S. tectonics: Southern Geology, v. 43, n. 2, p. 57-80. Perry, W. J., 1964, Geology of the Ray Sponaugle Mc Dowell, R. R., Matchen, D. L., Avary, K. L. well, Pendleton County, West Virginia: and Cook, T., 2000, Preliminary bedrock American Association of Petroleum geologic map of the Doe Hill Quadrangle, Geologists Bulletin, v. 48, n. 5, p. 659-669. Virginia and West Virginia: West Virginia Geologic and Economic Survey Open-file ______, 1979, The Wills Mountain Publication OF-9807, 1:24,000-scale map Anticline: a study in complex folding and and cross-sections. faulting in eastern West Virginia: West Virginia Geological and Economic Survey ______, compiler, 2001, Stratigraphic Report of Investigation No. RI-32, 29p. geochemical database for portions of Pendleton County, West Virginia and Pohn, H. A., de Witt, W., Jr., and Schultz, A. P., adjacent Virginia counties, covering 1985, Disturbed zones, lateral ramps and their portions of Pendleton County, West relationship to the structural framework of Virginia, Highland County, Virginia and the central Appalachians: AAPG Guidebook Augusta County, Virginia: West Virginia for field trip 3, Williamsburg, Virginia. Geologic and Economic Survey Report of Investigations 34, computer diskette. Rader, E. K., Gathright, T. M. and Marr, J. D., 1986, Trimble Knob basalt diatreme and ______, Matchen, D. L., Avary, K. L., associated dikes, Highland County, Virginia: Diecchio, R., Rutledge, F. A. and McCoy, Geological Society of America Centennial H. E., 2002, Preliminary bedrock geologic Field Guide- Southeastern Section, p. 97- map of the Snowy Mountain Quadrangle, 100. Virginia and West Virginia: West Virginia Geologic and Economic Survey Open-file PUBLICATION 178 19

Ramsey, E. W. A., 1950, Geology of the southern 33rd annual Virginia Geological Field portion of the Bolar Valley Anticline, Conference guidebook, 32 p. Highland County, Virginia: University of Virginia Masters thesis. ______, McDowell, R. R., Avary, K. L., Matchen, D. L. and Wilkes, G. P., 2004, Ressetar, R. and Martin D. L., 1980, Middle Eocene igneous rocks in the Valley Paleomagnetism of Eocene intrusions in and Ridge of Virginia and West Virginia, the Valley and Ridge province, Virginia and p. 137-161, in Southworth, S. and Burton, West Virginia: Canadian Journal of Earth W. (eds), 2004, Geology of the national Science, v. 17, p. 1583-1588. capitol region- field trip guidebook: U. S. Geological Survey Circular 1264, 298p. Southworth, C. S., Gray, K. J. and Sutter, J. F., 1993, Middle Eocene intrusive igneous Vogt, P. R., 1991, Bermuda and Appalachian- rocks of the central Appalachian Valley Labrador rises: Common hot-spot and Ridge province- setting, chemistry, processes?: Geology, v. 19, n. 1, p. 41-44. and implications for crustal structure: U. S. Geological Survey Bulletin 1839-J, 24 p. Whitelaw, B. and Hevener, R., 1994, Radon in caves?: Highland County High School, Swartz, F. M., 1929, The Helderburg Group in Monterey, Virginia, 16p. parts of West Virginia and Virginia: U. S. Geological Survey Professional Paper 158- Woodward, H. P., 1941, Silurian System of West C, p. 27- 77. Virginia: West Virginia Geological Survey, v. 14, 326 p. Sweet, P. C., 1981, High-silica resources in Augusta, Bath, Highland, and Rockbridge Zartman, R. E., Brock, M. R., Heyl, A. V. and Counties, Virginia: Virginia Division of Thomas, H. H., 1967, K-Ar and Rb-Sr ages Mineral Resources Publication 32, 22 p. of some alkaline intrusive rocks from central and eastern United States: American Journal ______, 1996, Diamonds in Virginia: of Science, v. 265, n. 10, p. 848- 870. Virginia Division of Mineral Resources Virginia Minerals, v. 42, n.4, pp. 33-40.

Tarleton, W. A., 1948, The geology of the southern portion of the Hightown anticline, Monterey quadrangle, Highland County, Virginia: University of Virginia Masters thesis.

Tso, J. L. and Surber, J. D., 2003, A field study of Eocene intrusive rocks and their surroundings in Highland County, Virginia: Abstracts with programs, Geological Society of America, v. 35, n. 1, p. 69.

______, McDowell, R. R., Avary, K. L., Matchen, D. L. and Wilkes, G. P., 2003, Middle Eocene igneous rocks in the Valley and Ridge of Virginia and West Virginia: Virginia Publication 178, Plate 1 Department of Mines, Minerals Geologic Map of the Monterey Quadrangle, Virginia and Energy Virginia Division of Geology and Mineral Resources GEOLOGIC MAP OF THE MONTEREY QUADRANGLE, VIRGINIA

(THORNWOOD) Gerald P. Wilkes DESCRIPTION OF MAP UNITS 2011 (CIRCLEVILLE) 79° 37’ 30’’ (SNOWY MOUNTAIN) 79° 30’ 00’’ 38° 30’ 00’’ 38° 30’ 00’’

Qal Qal - alluvium - light- to medium-gray silt, fine- to medium-grained sand, gravel QUATERNARY and cobbles.

a a - alkalic rock - fine- to coarse-grained, light- to medium-gray, massive, 80 to 90% plagioclase.

R-9166 m - mafic rock - fine-grained, dark gray to black, massive, may contain igneous ma & & xenoliths. EOCENE JURASSIC CENOZOIC Sw MESOZOIC R-9180 mb b - breccia - volcanic, dark-gray to black, poorly sorted xenoliths of sedimentary R-9167 and igneous rock within a fine- to coarse-grained matrix of variable composition.

Db Brallier Formation - siltstone, shale, and thin sandstone, olive-gray, micaceous, sparsely fossiliferous. Only the lowest few hundred feet are exposed in the quad- Sw rangle.

Sw Dmn Millboro Shale and Needmore Formation, Undivided R-9171-9175 Millboro - shale, black, fissle, near the base is an interval of thin limestone beds, dark-gray, aphanitic; Needmore - shale, olive-gray, calcareous, fossiliferous, readily weathered. Composite thickness 800 to 1200 feet.

-Unconformity-

Dr Ridgely Sandstone - sandstone, medium-gray, calcareously cemented, fine- to DEVONIAN coarse-grained, fossiliferous, most notably “Spirifer”. Includes . 100 feet thick.

DSh Helderburg Group

Sw Licking Creek Limestone - limestone, medium-gray, arenaceous, with white nodular chert, 100 feet thick; New Creek Limestone - limestone, gray to pink, coarse-grained, crinoidal, 50 feet thick; Keyser Formation - limestone, coarse- grained, nodular-weathering, arenaceous, 200 feet thick; Big Mountain Shale Member of the Keyser - shale, medium-gray to light-green, calcareous, found approximately mid-section, 50 feet thick.

Tonoloway Limestone and Wills Creek Formation Stw Tonoloway Limestone - consists of an upper and lower unit: limestone, dark- gray, fine-grained, thin-bedded; and a middle unit: limestone, thick-bedded, course-grained tempestites. Wills Creek Formation - shale, silty, gray green- weathering, with interbedded limestone, light gray, thin-bedded, fine-grained. Composite thickness of this map unit is 200 to 820 feet.

Sw Williamsport Sandstone - sandstone, thick-bedded, medium-grained, light-gray to white, indurated, fucoidal, 30 feet thick. The Williamsport is represented by the Sw contact line between adjacent units.

Smc McKenzie Formation - sandstone, calcareous, cross-bedded, with limestone, SILURIAN knobby-weathering, dark-gray, fossiliferous, 210 feet thick. Includes thin sandstone beds (including the Keefer Sandstone), white to light-gray, thick bedded, medium- to coarse-grained, up to 5 feet thick.

Srh Rose Hill Formation - sandstone, maroon, medium-grained, hemititic, well- indurated, and shale and siltstone, red, green, and gray, 200 to 250 feet thick. PALEOZOIC

Stu Tuscarora Formation - orthoquartzite and sandstone, white to light-gray, ledge- forming, medium- to coarse-grained, with quartz-pebble conglomerate in lower half of unit, 80 feet thick.

-Unconformity-

Oj Juniata Formation - Sandstone, fine-grained medium-bedded shale, and mudstone, red to olive-gray, 275 feet thick.

Sw Oro Reedsville Shale and Oswego Sandstone Reedsville Shale - shale and siltstone, calcareous, yellow-gray, green-gray, and medium-gray, Orthorhynchula zone near top of unit. Oswego Sandstone: (HIGHTOWN) sandstone, brown, medium- to coarse-grained, and shale partings, gray and green, R-9185 R-9187 (DOE HILL) 50 feet thick. Composite thickness is 1200 feet.

Odr Dolly Ridge Formation - limestone, medium-gray, knobby- and wavy-bedded,

Sw fine-grained, 300 feet thick.

Middle Ordovician, Upper Member - limestone, light-gray, wavy-bedded, R-9151 R-9169 Omu R-9188 medium- to coarse-grained, 50 feet thick. R-9150

ORDOVICIAN Middle Ordovician, Middle Member - limestone, medium- to dark-gray, micro- Omm R-9152 R-9160 to very fine-grained, thick-bedded, 180 feet thick.

Middle Ordovician Lower Member - limestone and dolostone, medium-gray, Oml medium- to thin- and wavy- bedded, fossiliferous, 100 feet thick.

R-9163 R-9168 -Unconformity- R-9153 R-9156 R-9182 R-9158 R-9184 Ob Beekmantown Formation - dolostone, light- to medium-gray, thick-bedded, fine-grained, distinctive “butcher-block” jointing on some weathered surfaces, black bedded chert, beds of white massive chert near top of unit, with some interbeds of limestone, light-to medium-gray. Only the upper few hundred feet are exposed in the quadrange.

Sw Conocheage Formation - interbeded dolostone, limestone and sandstone, dark- O|co R-9178 to medium-gran, medium- to thin-beded, finegrained, interpreted presence in cross-section, not exposed on surface. Sw R-1954 Sw

R-9179 MAP SYMBOLS

For contact, and fault symbols: lines are solid where the location is exact, long- dashed where the location is approximate, short-dashed where the location is inferred, and dotted where the location is concealed. R-9157

Sw

Sw

R-9170 R-1861

R-9181

Sw

Sw

R-9163 R-9186

38° 22’ 30’’ R-9164 38° 22’ 30’’ 79° 37’ 30’’ (MONTEREY SE) 79° 30’ 00’’ (MC DOWELL)

Basemap modified from U.S. Geological Survey DRG SCALE 1:24000 MN (MUSTOE) 1 0.5 0 1 MILE GN 1969, Monterey Quadrangle, Virginia 1000 0 1000 2000 3000 4000 5000 6000 7000 FEET o 8 58’ o ' 1 0.5 0 1 KILOMETER 158 MILS 0 54 Projection: Polyconic 16 MILS NAD 1927 Datum CONTOUR INTERVAL 40 FEET NATIONAL GEODETIC VERTICAL DATUM OF 1929

Surficial Geology and Digital Cartography by Jason Elliott 2010 MAGNETIC NORTH DECLINATION AT CENTER OF SHEET

Interpretive cross-section Subsurface structures interpreted from surface measurements.