Editing Chimney Rock, North Carolina (section)

==Geology==
Geological mapping by Hadley and Nelson<ref name="HadleyOthers1971a"/> and Robinson and others<ref name="RobinsonOthers1979a"/> found that the Henderson Gneiss underlies the mountains, hills, and valley in the region of Chimney Rock and parts of adjacent Chimney Rock State Park. The Henderson Gneiss is a medium- to coarse-grained, generally well-[[Foliation|foliated]], [[biotite]]-[[microcline]] [[augen]] [[gneiss]]. It is finer grained and more foliated adjacent to the [[Brevard Fault]] zone and becomes coarser and less foliated towards the southeast.<ref name="Eppes2022a"/><ref name="HadleyOthers1971a">Hadley, J.B., and Nelson, A.E., 1971. ''Geologic map of the Knoxville quadrangle, North Carolina, Tennessee, and South Carolina''. ''U.S. Geological Survey, Miscellaneous Geologic Investigations Map'', I-654, scale 1:250,000.</ref><ref name="RobinsonOthers1979a">Robinson, G.R., Lesure, F.G., Marlow, J.I., Foley, N.K., and Clark, S.H., 1979. [https://ngmdb.usgs.gov/Prodesc/proddesc_63783.htm ''Bedrock geology and mineral resources of the Knoxville 1 degree X 2 degree quadrangle, Tennessee, North Carolina, and South Carolina'']. U.S. ''Geological Survey, Open-File Report'', OF-2004-1075, scale 1:250,000.</ref> Where [[Radiometric dating|radiometrically dated]], the Henderson Gneiss yielded an [[Rubidium–strontium dating|Rb-Sr whole-rock age]] of 535+27 [[Year#Megaannus|Ma]] and [[Uranium–lead dating|U-Pb]] [[zircon]] ages of 592 and 538 Ma.<ref name="RobinsonOthers1979a"/><ref name="OdumOthers1973a">Odum, A.L., and Fullagar, P.D., 1973. ''Geochronologic and tectonic relationships between the Inner Piedmont, Brevard zones, and Blue Ridge belts, North Carolina''. ''American Journal of Science'', 73-A, pp. 133-149.</ref><ref name="SinhaOthers1978a">Sinha, A.K., and Glover, L., 1978. ''U-Pb systematics of zircons during dynamic metamorphism.'' ''Contributions to Mineralogy and Petrology'', 66, pp. 305-310.</ref> Near Bat Cave, North Carolina, a couple of ([[Triassic]] ?) [[diorite]] [[Dike (geology)|dikes]] have been mapped cutting through the Henderson Gneiss west of Chimney Rock. The Henderson Gneiss lacks any cross-cutting [[pegmatite]] dikes and associated economic mineral deposits in the region of Chimney Rock and Bat Cave. The closest pegematite dikes, which lack any observed, commercial mineral deposits, occur in [[biotite]]-[[muscovite]] granitic gneiss forming the upper part of Sugarloaf Mountain.<ref name="Eppes2022a"/><ref name="RobinsonOthers1979a"/><ref name="Lemmon Others1973a">Lemmon, R.E., and Dunn, D.E., 1973. [https://www.deq.nc.gov/energy-mineral-and-land-resources/geological-survey/assorted-maps/geologic-map-and-mineral-resources-summary-bat-cave-quadrangle-nc/open ''Geologic map and mineral resources summary of the Bat Cave quadrangle, North Carolina''.] ''North Carolina Geological Survey, Geologic Map - 7.5-minute quadrangle maps and mineral resource summary''. GM 202-NE, scale 1:24,000.</ref>

The Chimney Rock - Hickory Nut Gorge area is part of a block of crust known now as the Tugaloo terrane. This piece of crust was a [[microcontinent]] that collided and accreted to North America during the [[Cambrian]] and early [[Ordovician]] periods. It was at this time that massive amounts of [[granodiorite]]s, including the precursor [[plutonic]] rocks to the Henderson Gneiss, [[Intrusive rock|intruded]] into metasedimentary rocks at approximately 448 Ma. During this and later times, the rocks of the Tugaloo terrane experienced multiple periods intense [[Fold (geology)|folding]], faulting, and metamorphism. Between 390 and 340 Ma, the granodiorites were altered by a period of intense  [[metamorphism]] and [[Thrust fault|thrust faulting]] to form the Henderson Gneiss and the gently dipping northeast-southwest trending foliation and folding associated with it.<ref name="Eppes2022a"/><ref name="MoecherOthers2011a">Moecher, D., Hietpas, J., Samson, S., and Chakraborty, S., 2011. ''Insights into southern Appalachian tectonics from ages of detrital monazite and zircon in modern alluvium''.  ''Geosphere'', 7(2) pp. 1–19.</ref><ref name="HillOthers2024a">Hill, J., Wooten, R., Cattanach, B., Bauer, J., Bozdog, N., Douglas, T., Isard, S., Khashchevskaya, D., Korte, D., Kuhne, J., Owen, L., Prince, P., Scheip, C., Waters-Tormey, C., and Wegmann, K., 2024. [https://pubs.geoscienceworld.org/gsa/books/edited-volume/2621/chapter/143104651/Big-slow-movers-debris-slides-and-flows-and-mega ''Big slow-movers, debris slides and flows, and mega-boulders of the Blue Ridge Escarpment, western North Carolina, USA''.] In Merschat, A.J., and Carter, M.W., eds., pp. 13–67, [https://pubs.geoscienceworld.org/gsa/books/edited-volume/2621/Geology-and-Geologic-Hazards-of-the-Blue-Ridge ''Geology and Geologic Hazards of the Blue Ridge: Field Excursions for the 2024 GSA Southeastern Section Meeting, Asheville, North Carolina, USA''.] ''Geological Society of America Field Guide'', 67 106 pp. {{ISBN|978-0-813-70067-0}}</ref>

During the post-[[Paleozoic]], stresses caused by the uplift, erosion, and decompression of the Henderson Gneiss fractured it into orthogonal, sub-vertical [[Joint (geology)|joints]]. The timing of formation of these joints is poorly constrained. They typically occur as west-northwest - east-southeast and north-northeast - south-southwest systematic set of joints. These joint sets lie parallel and perpendicular to the Hickory Nut Gorge and define the rectilinear drainage networks. Because of a regional humid climate and steep gorge walls composed of systematically jointed and fractured bedrock, Hickory Nut Gorge has a long record of historical landslide events.<ref name="Eppes2022a"/><ref name="HillOthers2024a"/> These events include those in 1916, 1994, 1996, 2008, 2012, 2013, and 2018 as documented in the North Carolina Geological Survey's ''Western North Carolina Landslide Hazard Viewer''.<ref name="NCGS2024a">North Carolina Geological Survey, 2024. [https://www.deq.nc.gov/about/divisions/energy-mineral-and-land-resources/north-carolina-geological-survey/geologic-hazards/landslides ''Landslides - Introduction to landslides in North Carolina.''] Last retrieved October 10, 2024.</ref><ref name="NCGS2024b">North Carolina Geological Survey, 2024. [https://experience.arcgis.com/experience/b55c8497d115400aa09d9cb7a27f5dc8/page/page_7/ ''Western North Carolina Landslide Hazard Data Viewer.''] Last retrieved October 10, 2024.</ref> The presence of extensive rock boulder and block deposits at the base the gorge's wall show that [[debris flow]]s and [[rock fall]]s have been active along the steep gorge walls throughout the [[Quaternary]].<ref name="Eppes2022a"/>