Editing Mount Umunhum (section)

==Geology==
Mount Umunhum consists of a [[Geological formation|geologic formation]] that is known as the ''[[Coast Range Ophiolite]].'' This [[ophiolite]] is a piece of Middle [[Jurassic]] [[oceanic crust]] and [[Mantle (geology)|mantle]] that has been [[obduction|obducted]] onto land and largely been converted to [[serpentinite]]. It has been extensively [[Fault (geology)|faulted]] and [[diapir]]ically [[Geologic uplift|uplifted]] and [[erosion|eroded]] to form Mt. Umunhum and extensive [[outcrop]] areas throughout the Santa Cruz Mountain foothills and elsewhere. The Coast Range Ophiolite is also known to underlie the rocks of the Great Valley throughout central California. The exposure on the northeast face of Mt. Umunhum is one of the best Bay Area exposures of the Coast Range Ophiolite.<ref name="BaileyOthers1970a">Bailey, E. H., Blake Jr, M. C., and Jones, D. L. (1970). ''On-land Mesozoic oceanic crust in California coast ranges.'' ''[https://pubs.usgs.gov/pp/0700c/report.pdf US Geological Survey Professional Paper]'', 700, C70-C81.</ref><ref name="StofferOthers2002a">Stoffer, P. W. and Messina, P. (2002). [https://pubs.usgs.gov/of/2002/0121/pdf/of02-121.pdf ''Field-Trip Guide to the Southeastern Foothills of the Santa Cruz Mountains In Santa Clara County, California.''] ''US Geological Survey Open-File Report'', 2, p. 121.</ref>

Mount Umunhum and nearby [[Loma Prieta]] are pushed upward by local collision forces associated with a left bend in the [[San Andreas Fault]].  Starting near [[Uvas Canyon]], the fault stops trending northwest but instead bends west-northwest for about eight miles before continuing its northwest direction.  This left bend is renowned among geologists as an archetypal [[restraining bend]] which acts to oppose [[strike-slip]] motion along the fault.<ref name="Abstract ID T43E-02">{{cite journal |title=Exhumation history of the Sierra Azul Block of the Santa Cruz Mountains Revealed Using Low Temperature Thermochronology |journal= American Geophysical Union, Fall Meeting 2008 |date=December 2008 |last1=Hilley |first1=G.E. |last2=Dumitru |first2=T. |last3=Gudmundsdottir |first3=M.H. |last4=Burgmann |first4=R. |bibcode=2008AGUFM.T43E..02H |url=https://ui.adsabs.harvard.edu/abs/2008AGUFM.T43E..02H/abstract |accessdate=2022-10-01 }}</ref> From the perspective of Mount Umunhum and other mountains atop the [[Sierra Azul block]], the [[Pacific Plate]] is trying to shear them off the [[North American Plate]] but can't break them off.  Rather, the resulting [[transpression]] force pushes up the local terrain and helps explain why these are the highest peaks in the [[Santa Cruz Mountains]].<ref>{{cite book |last1=Sloan |first1=Doris |title=Geology of the San Francisco Bay Region |location=Berkeley, California |publisher=University of California Press |year=2006 |page=43 |isbn=978-0-520-24126-8 }}</ref>