Simi Valley (valley)

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Coordinates: 34°16′42″N 118°42′39″W / 34.27833°N 118.71083°W / 34.27833; -118.71083
Source: Wikipedia, the free encyclopedia.
For the city, see Simi Valley, California.
The Simi Valley as seen from Sage Ranch Park.

Simi Valley (Chumash: Shimiyi)[1][2][3] is a synclinal valley in Southern California in the United States. It is an enclosed or hidden valley surrounded by mountains and hills. It is connected to the San Fernando Valley to the east by the Santa Susana Pass and the 118 (Ronald Reagan) freeway, and in the west the narrows of the Arroyo Simi and the Reagan Freeway connection to Moorpark. The relatively flat bottom of the valley contains soils formed from shales, sandstones, and conglomerates eroded from the surrounding hills of the Santa Susana Mountains to the north, which separate Simi Valley from the Santa Clara River Valley, and the Simi Hills.[4]

Geology

U.S. Highway 101 and state highways 118, 23, and 126
provides access to the area. Current land use includes citrus and avocado orchards, oil well drilling and production, sand and gravel quarries, decorative-rock quarries, cattle grazing, suburban residential development, and golf courses. The oldest geologic unit mapped in the Simi Valley quadrangle is the upper
Vaqueros Formation that is composed of transitional and marine sandstone, siltstone, and claystone with local sandy coquina beds.[6] In the Las Posas Hills, Sespe Formation is unconformably overlain by marine sandstones of the middle Miocene Topanga Group that are interlayered with and intruded by basalt flows, breccia, and diabase dikes of the Conejo Volcanics.[7]

Suburban development in Simi Valley

Deep-marine strata of the upper Miocene Modelo Formation cover the Vaqueros Formation and Topanga Group along the crests and southern flanks of South Mountain and Oak Ridge. They also occur as isolated outcrops in the Las Posas Hills. Locally, Modelo Formation consists of interbedded diatomaceous shale, claystone, mudstone, and siltstone with minor sandstone, limestone, chert, and tuff beds. The most widely exposed rock units in the area are the Plio-Pleistocene marine and non-marine Pico and Saugus Formations that crop out on the southern flank of South Mountain-Oak Ridge. Locally, the Pico Formation consists of marine siltstone and silty shale with minor sandstone and pebbly sandstone. The Saugus Formation overlies and interfingers with the Pico Formation and is composed of interbedded shallow-marine to brackish water sandstone, siltstone, pebble-to-cobble conglomerate, and coquina beds that grade laterally and vertically into non-marine sandstone, siltstone, and conglomerate. A local member of the Saugus Formation is exposed in the southwest corner of the map area. It is predominantly a volcanic breccia conglomerate that resembles the Conejo Volcanics breccia, but is believed to represent remnants of landslide debris shed from the Conejo Volcanics into a local trough during Saugus time.[8]

Valley surficial deposits cover the floor and margins of the Little Simi Valley,

Topanga and Modelo Formations) trace southward to outcrops in the Santa Monica Mountains that constrain faulting along the valley's south basin edge. Cretaceous strata in the Simi Uplift to the west are over 2 km higher than equivalent strata beneath the western San Fernando Valley across a boundary marked by the Chatsworth Reservoir fault, and Neogene thinning and off-lap. The Simi fault, located at the eastern end of the Simi-Santa Rosa fault system, bounds the northern margins of the Simi and Tierra Rejada Valleys. West of Simi Valley, the Simi fault has placed Miocene Conejo Volcanics over Plio-Pleistocene Saugus Formation rocks. The 15.5 ± 0.8 m.y.a. base of the Conejo Volcanics, identified in oil well logs, is inferred to have a dip-slip separation of about 425 to 550 m, suggesting a low long-term slip rate of about 0.03 mm/yr. However, substantial late Quaternary offset is suggested by the presence of more than 150 m of Pleistocene and younger alluvium that fills the east-west trending, down-dropped bedrock trough beneath western Simi Valley. In addition, trenching within faulted colluvial deposits in Tierra Rejada Valley has revealed evidence of multiple shears within Holocene deposits.[9]

References

  1. ISBN 978-0-945092-23-0
    .
  2. ISBN 978-0965944212
    .
  3. ^ Metcalfe, Coll (April 24, 1998). "When It Comes to Saying Simi, There's a Pronounced Difference". Los Angeles Times.
  4. ^ U.S. Geological Survey Geographic Names Information System: Simi Valley
  5. USGS
    .
  6. ^ Harris, Mike (October 26, 2019). "July earthquakes reveal 15-million-year-old fossil in Simi Valley thought to be small whale". Ventura County Star.
  7. ^ Darton, Nelson Horatio (1915). Guidebook of the Western United States. U.S. Government Printing Office. Pages 100-102.
  8. ^ Blake, Thomas F. (1991). Engineering geology along the Simi-Santa Rosa Fault system and adjacent areas, Simi Valley to Camarillo, Ventura County, California: field trip guidebook : 1991 Annual Field Trip, Southern California Section, Association of Engineering Geologists, Volume 2. Association of Engineering Geologists. Pages 209-267.
  9. U.S. Geological Survey
    . Open-File Report 97-259.
  • Glendinning, R. M. (1938), "The Simi Valley, California", The Geographical Journal, 92 (6): 527–536,
    JSTOR 1788136

34°16′42″N 118°42′39″W / 34.27833°N 118.71083°W / 34.27833; -118.71083

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