ABSTRACT Two construction aggregate companies, Cemex and Hanson Aggregates, operate respective crushed stone quarries on the east and west slopes of Mount Zion in Clayton, California. These sidehill quarries utilize a single highwall and mine Jurassic diabase of the Coast Range ophiolite that formed as a sheeted dike complex. Hydrothermal veins, some containing 20%–30% disseminated pyrite and chalcopyrite, cut the diabase. The east quarry, operated by Cemex, was started by the Harrison-Birdwell Company in 1947. The west quarry, operated by Hanson, was started by the Henry J. Kaiser Sand and Gravel Company in 1954. The Cemex quarry highwall is visible as you come into the city of Clayton on Marsh Creek Road, with a height of ~280 m (920 ft). The height of the highwall at the Hanson quarry is ~215 m (700 ft). Both operations remove weathered diabase overburden to expose fresh diabase, which is drilled, blasted, and hauled to the plant for processing. To ensure aggregate is suitable for construction, quality assurance testing is conducted in accordance with the specifications of various agencies. These quarries supply the surrounding area with aggregate for hospitals, schools, highways, dams, and other buildings. Noteworthy projects supplied by the Clayton quarries include the Concord BART Station, Interstate-680, Interstate-580, Calaveras Dam, Sherman Island Levee, Highway 4, Highway 24, and Bay Bridge epoxy asphalt. Before aggregate was mined, Mount Zion was the site of a copper rush from 1862 to 1864. Gold and silver were also reported in various assays from the Clayton district. Although prospecting created excitement around Clayton, no productive orebodies were ever discovered.

ABSTRACT The Cemex Inc. limestone quarries are located in the Sidewinder Mountain–Black Mountain area northeast of Victorville in the Mojave Desert, California. Bedrock in this area includes Neoproterozoic and Paleozoic miogeoclinal carbonate-dominated metasedimentary roof pendants, and is the type location of the Jurassic Fairview Valley Formation, an overlying unnamed quartzite unit, and the Jurassic Sidewinder volcanic rocks. A variety of Triassic, Jurassic, and Cretaceous intrusive rocks and dikes also are abundantly exposed. Complex geologic structure in the area resulted from a prolonged geologic history that includes multiple Permian–Triassic and Mesozoic contractional, metamorphic, intrusive, and extensional deformation events, and younger Cenozoic deformation that has continued into recent time. Permian–Triassic deformation includes complex polyphase deformation and metamorphism of Paleozoic rocks, and intrusion of Triassic monzonite, followed by uplift and erosion. Lower Jurassic Fairview Valley Formation unconformably overlies Paleozoic rocks and Triassic monzonite and was largely derived from them. The Fairview Valley Formation was deformed and eroded prior to juxtaposition with overlying quartzite. Overlying the quartzite are Middle Jurassic Lower Sidewinder Volcanic rocks (181–165 Ma). During and following Lower Sidewinder volcanism, faulting related to regional caldera collapse events occurred. Extensional deformation occurred prior to and after intrusion of late Middle Jurassic granitic rocks. Northwest-trending dikes correlated with the Late Jurassic Independence dikes cut previously juxtaposed Fairview Valley Formation, quartzite, and Lower Sidewinder Volcanics. During Cretaceous time, intrusion of quartz monzonite plutonic rocks occurred. The Helendale fault, one of several active major northwest-striking faults of the Eastern California shear zone, has been traced for ~90 km and passes within 2 km of the Cemex operations. The location of the Helendale fault zone is thought to be a long-lived zone of structural weakness. Recurrent surface rupture along the modern Helendale fault in Holocene and recent time (200–10,000 yr) has been documented. Data suggest that right-stepping en echelon strands formed a pull-apart basin as much as 3 km wide in the Fairview Valley area, with up to 3 km of right lateral offset. The Cemex Inc. cement production facility is the largest in California. Deposits mined include the Reserve (White Mountain) quarry and the Black Mountain quarry. The Reserve quarry produced an estimated 25 million tons of calcite marble between the early 1940s and late 1970s. The deposit located on the south slope of Black Mountain was formed from metamorphosed Upper Paleozoic limestones. The Black Mountain quarry was opened in the early 1950s and originally formed a mountain. Currently, the quarry is an open pit ~1200 m long, 800 m wide, and >60 m deep. Production is estimated at 4 million tons per yr. Cement-grade ore mined at the Black Mountain quarry is limestone-cobble conglomerate of the upper member of the Jurassic Fairview Valley Formation, which was derived from the Pennsylvanian–Permian Bird Spring Formation, and only occurs in the quarry area. The deposit is folded into a tight northwest-trending syncline and bounded to the south, east, and north by faults. This unique deposit is suitable as a long-term (>100 yr) source of limestone for cement manufacture.

Abstract The Silurian rocks of the Cincinnati Arch in Ohio, Kentucky, and Indiana have been studied for nearly two centuries. Compilation of data from these studies, combined with detailed analysis of nearly 20 continuous drill cores and remeasuring and resampling of more than 60 major outcrops, is the basis for a high-resolution sequence stratigraphic framework. Seven depositional sequences are assigned on the basis of through-going unconformities, which mirror those already recognized in the early Llandovery to early Ludlow of the northern Appalachian Basin. Revision of the conodont biostratigraphy for the Cincinnati Arch has produced results that both agree and disagree with the other lines of data implemented in the sequence stratigraphic depositional model. Biostratigraphic correlations between southern Ohio and the Niagara Falls area are largely in agreement with correlations based on other lines of data, as are correlations between west-central and western Ohio, southeastern Indiana, and northern Kentucky. However, correlations between southern and west-central Ohio show major areas of disagreement. Preliminary whole rock carbonate carbon isotope analyses in western-central Ohio show patterns roughly comparable to those documented in the Niagara region, Gotland, and elsewhere. Chemostratigraphic data that might resolve inconsistencies in the correlations between southern and west-central Ohio were not yet available at the time of publication.

Abstract This field guide focuses on key outcrops that highlight recent nomenclatorial changes of Early Silurian strata in western Ohio (e.g., Dayton Formation, Osgood Formation, Laurel Formation, Lewisburg Formation, Massie Formation, Euphemia Dolomite), as well as the Brassfield Formation and Springfield Dolomite. The field trip begins near the apex of the Cincinnati/Findlay Arch at a quarry in Ludlow Falls, Ohio, and ends at a more offshore position to the southeast, near Clifton, Ohio. Recent conodont biostratigraphic and δ 13 C carb chemostratigraphic data for many of those formations at the field trip localities clearly demonstrate coeval stratigraphic patterns present throughout western Ohio that were previously obscured due to prior inconsistent lithostratigraphic terminology and correlation. Those data also help to show important differences in stratigraphic patterns in western Ohio. Strata correlative to the Lee Creek Formation are recognized for the first time near the apex of the Cincinnati/Findlay Arch in western Ohio in West Milton, Ohio, and are tentatively identified as that formation. At the same locality the Dayton is shown to be completely absent, and the Osgood Formation overlies a thin unit tentatively identified as the Lee Creek Formation and underlying Brassfield Formation. The Springfield Dolomite at the Barrett Paving Materials Ludlow Quarry in Ludlow Falls, Ohio, contains trilobites of the Gravicalymene celebra Association, one of the most taxonomi-cally diverse and geographically widespread trilobite associations in the Silurian of North America. Pentamerid brachiopods occur with molts of Gravicalymene celebra in the Springfield there, suggesting an environmental complexity not seen elsewhere; pentamerids are not found in strata containing the Gravicalymene celebra Association in most other areas of the Midwest.

Abstract This article is aimed at providing an overview of the geology of the Dayton region to those who seek an introduction to Dayton’s geological story. The oldest rocks exposed in the area are Ordovician (Katian Stage, Cincinnatian Series in local North American usage) in age, and are world famous for the quantity and quality of their fossils. Unconformably overlying the Ordovician strata are Silurian (Llandovery–Wenlock Series) dolomites, limestones, and shales, which represent tropical seas that were at times rich in crinoids, corals, brachiopods, and other invertebrates. A large time gap (unconformity) in the rock record of some 420+ million years occurs between the Silurian and the Pleistocene “Ice Age” deposits of the area. Significant changes to the natural environment in the Dayton area have occurred during the Anthropocene. A number of localities that can be reached within about 30–40 minutes from downtown Dayton are described. This is effectively Montgomery County and adjacent counties. As such this treatment is brief and not meant as a compendium but as an introduction and outline of Dayton’s geology and geological history. The localities selected illustrate Dayton’s geological heritage, from the Ordovician to the Pleistocene, while several of the area’s distinctive natural landmarks are discussed. A number of the landforms are expressions of the Niagara Escarpment, where resistant Silurian limestones and dolomites overlie less resistant older rocks.

Abstract Two continuous gas assessment units (AU’s) are present in the Late Triassic (Norian) onshore rift basins of North Carolina and south-central Virginia. Continuous AU’s are the USGS classification/nomenclature for the oil and gas rich resource plays industry has been pursuing and exploiting throughout the continental United States. “Continuous gas assessment units” include tight gas sandstone as well as two resource plays—coal-bed methane and shale gas/oil. The USGS assessed the East Coast Mesozoic rift basins as continuous gas AU’s primarily as tight gas AU’s because oil and gas have been found (although not produced) from tight ( i.e. , low porosity and permeability) sandstones, coal beds, and shale beds/intervals. The source rocks are lacustrine shales that were deposited in freshwater lakes that were near the paleo-equator after the onset of Pangea rifting. These two rift basins, the Deep River basin wholly within North Carolina, and the Dan River-Danville basin, located in north-central North Carolina and south-central Virginia have been assessed numerically as part of the USGS’s National Petroleum Resource Assessment ( Fig. 1 ). The name ‘Dan River-Danville basin’ is used by the U.S. Geological Assessment team for assessment, and the name, ‘Dan River basin’ is used herein following stratigraphic revision and formal basin naming in 2015 ( Olsen et al. , 2015 ). These two rift basins are part of a series of larger continental series rift basins that formed during the Permian to Early Jurassic extension in central Pangea as the supercontinent began to fragment. Figure 1. Map of the Eastern United States showing the location of the five quantitatively (volumetrically) assessed East Coast Mesozoic basins (in red), the nine basins that were not volumetrically assessed (in orange), and the U.S. Geological Survey province boundaries. Each basin includes a single continuous gas assessment unit ( Milici et al. , 2012 ). These continuous gasprone AUs each have a single total petroleum system (TPS). The Deep River basin continuous AU has an estimated mean gas content of 1,660 billion cubic feet of gas (BCFG) and an estimated mean of 83 million barrels of natural gas liquids (MMBNGL). Noble gases have been documented from two shut-in wells in the Deep River basin by the North Carolina Geological Survey in a separate study ( Reid et al. , 2015c ). The Dan River-Danville basin continuous AU has an estimated mean gas content 49 BCFG and no natural gas liquids from data available in 2011 assessed by the U.S. Geological Survey ( Milici et al. , 2012 ) ( Table 1 ). Table 1. East Coast Mesozoic basin assessment results ( Milici et al. , 2012 ). The Deep River basin composite TPS and the Dan River-Danville basin composite TPS assessment results and data for other basins. Note - MMBO, millions of barrels of oil; BCFG, billion cubic feet of gas; MMBNGL, million barrels of natural gas liquids; TPS total petroleum system; AU, assessment unit. Results in the table are fully risked estimates. For gas accumulations, all liquids are included as NGL (natural gas liquids). F95 represents a 95-percent chance of at least the amount tabulated; other fractiles are defined similarly. Fractiles are additive under the assumption of perfect positive correlation. Gray shading indicates not applicable ( Milici et al. , 2012 ). The Dan River basin stratigraphy has been clarified by Olsen et al. (2015) . A continuous 1,477-foot-deep stratigraphic core hole drilled in 2015 by the North Carolina Geological Survey penetrated a 323-ft-thick unconventional lacustrine shale reservoir containing a 3-ft-thick coal having gas shows in the coal and lower siltstone and then drilled through an underlying siliciclastic formation containing previously unknown thin organic strata, to basement at a depth of 1,451.2 ft below the surface. The Cumberland-Marlboro ‘basin,’ a large, strike-parallel and seaward negative aeromagnetic anomaly that is buried beneath thin unconsolidated coastal plain sediments, also was drilled and cored (three Rotasonic holes) in 2015 by the North Carolina Geological Survey. Metasedimentary Paleozoic(?) basement rock was recovered; no Triassic strata were present. Additional information that accompanies this extended abstract is found in Appendices 1–3.

ABSTRACT Franciscan subduction complex rocks of Mount Diablo form a 8.5 by 4.5 km tectonic window, elongated E-W and fault-bounded to the north and south by rocks of the Coast Range ophiolite and Great Valley Group, respectively, which lack the burial metamorphism and deformation displayed by the Franciscan complex. Most of the Franciscan complex consists of a stack of lawsonite-albite–facies pillow basalt overlain successively by chert and clastic sedimentary rocks, repeated by faults at hundreds of meters to <1 m spacing. Widely distributed mélange zones from 0.5 to 300 m thick containing high-grade (including amphibolite and eclogite) assemblages and other exotic blocks, up to 120 m size, form a small fraction of exposures. Nearly all clastic rocks have a foliation, parallel to faults that repeat the various lithologies, whereas chert and basalt lack foliation. Lawsonite grew parallel to foliation and as later grains across foliation. The Franciscan-bounding faults, collectively called the Coast Range fault, strike ENE to WNW and dip northward at low to moderate average angles and collectively form a south-vergent overturned anticline. Splays of the Coast Range fault also cut into the Franciscan strata and Coast Range ophiolite and locally form the Coast Range ophiolite–Great Valley Group boundary. Dip discordance between the Coast Range fault and overlying Great Valley Group strata indicates that the northern and southern Coast Range fault segments were normal faults with opposite dip directions, forming a structural dome. These relationships suggest accretion and fault stacking of the Franciscan complex, followed by exhumation along the Coast Range fault and then folding of the Coast Range fault.