Geomorphic indicators of active fold growth: South Mountain–Oak Ridge anticline, Ventura basin, southern California

Research Article| June 01, 2002 Geomorphic indicators of active fold growth: South Mountain–Oak Ridge anticline, Ventura basin, southern California Antonio Azor; Antonio Azor 1Departamento de Geodinámica, Universidad de Granada, Campus de Fuentenueva, E-18002 Granada, Spain Search for other works by this author on: GSW Google Scholar Edward A. Keller; Edward A. Keller 2Department of Geological Sciences and Institute for Crustal Studies, University of California, Santa Barbara, California 93106, USA Search for other works by this author on: GSW Google Scholar Robert S. Yeats Robert S. Yeats 3Department of Geosciences, Oregon State University, 104 Wilkinson Hall, Corvallis, Oregon 97331-5506, USA Search for other works by this author on: GSW Google Scholar GSA Bulletin (2002) 114 (6): 745–753. https://doi.org/10.1130/0016-7606(2002)1142.0.CO;2 Article history received: 25 Sep 2001 rev-recd: 22 Jan 2002 accepted: 22 Jan 2002 first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Antonio Azor, Edward A. Keller, Robert S. Yeats; Geomorphic indicators of active fold growth: South Mountain–Oak Ridge anticline, Ventura basin, southern California. GSA Bulletin 2002;; 114 (6): 745–753. doi: https://doi.org/10.1130/0016-7606(2002)1142.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract South Mountain–Oak Ridge, near Ventura, California, is an asymmetric anticlinal uplift forming at the present time above the active, buried Oak Ridge reverse fault. Shortening along the Oak Ridge fault accumulated largely in Quaternary time and is responsible for the growth and present topography of the westernmost 15 km of the ridge during the past 0.5 m.y. Tectonic geomorphic analysis using several indices of active tectonics provides information concerning fold growth. Stream-gradient indices are relatively high in the northern, eroded fold scarp of the ridge, a pattern consistent with the existence of active, rapid slip on the Oak Ridge fault. Mountain-front sinuosity along the northern slope of the anticlinal ridge roughly decreases from ∼2 to 1 toward the westernmost 10 km of observed surface folding. Valley floor width to valley height ratios along the northern flank of the ridge generally decrease westward from ∼1.5 to 0.5. Values of the hypsometric integral along the northern flank increase significantly from ∼0.35 to 0.4 (maximum ∼0.55) from east to west. Drainage density varies from ∼4 to 6 km/km2 along both flanks of the South Mountain–Oak Ridge anticline. Entrenchment of streams into the (southern) backlimb of the fold along the westernmost 9 km of the structure decreases from ∼20 m to <1 m from east to west. Apparent backlimb rotation, as measured by dip of strata along the westernmost 7 km of the fold, decreases from east to west, from ∼35° to 20°.Fold growth of the South Mountain–Oak Ridge anticline occurred during the past 0.5 Ma following deposition of the Saugus Formation. Lateral and vertical fold growth were likely produced by westward decrease in fault slip along the buried Oak Ridge fault. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.