page_title: Petroleum seep
section_title: California seeps
hierarchical_section_title: Petroleum seep / California seeps
caption_attribution_description: English: Oil seep in the Simi Valley area of Ventura County
context_page_description: A petroleum seep is a place where natural liquid or gaseous hydrocarbons escape to the earth's atmosphere and surface, normally under low pressure or flow. Seeps generally occur above either terrestrial or offshore petroleum accumulation structures. The hydrocarbons may escape along geological layers, or across them through fractures and fissures in the rock, or directly from an outcrop of oil-bearing rock.
  Petroleum seeps are quite common in many areas of the world, and have been exploited by mankind since paleolithic times. Natural products associated with these seeps include bitumen, pitch, asphalt and tar. In locations where seeps of natural gas are sufficiently large, natural "eternal flames" often persist. The occurrence of surface petroleum was often included in location names that developed; these locations are also associated with early oil and gas exploitation as well as scientific and technological developments, which have grown into the petroleum industry.
context_section_description: California has several hundred naturally occurring seeps, found in 28 counties across the state. Much of the petroleum discovered in California during the 19th century was from observations of seeps. The world's largest natural oil seepage is Coal Oil Point in the Santa Barbara Channel, California. Three of the better known tar seep locations in California are McKittrick Tar Pits, Carpinteria Tar Pits and the La Brea Tar Pits.
  At Kern River Oil Field, there are no currently active seeps. However, oil-stained formations in the outcrops remain from previously active seeps. Petroleum seeps may be a significant source of pollution.
  Seeps known as the McKittrick Tar Pits occur in the McKittrick Oil Field in western Kern County. Some of the seeps occur in watersheds that drain toward the San Joaquin Valley floor. These seeps were originally mined for asphalt by Native Americans, and in the 1870s larger scale mining was undertaken by means of both open pits and shafts.  In 1893, Southern Pacific Railroad constructed a line to Asphalto, two miles from present day McKittrick. Fuel oil for the railroad was highly desired, especially since there are very few coal-bearing formations in California.  The field is produced now by conventional oil wells, as well as by steam fracturing.
  The oil seeps at McKittrick are located in diatomite formation that has been thrust faulted over the younger sandstone formations.  Similarly, in the Upper Ojai Valley in Ventura County, tar seeps are aligned with east-west faulting.  In the same area, Sulphur Mountain is named for the hydrogen sulfide-laden springs.  The oil fields in the Sulphur Mountain area date from the 1870s.  Production was from tunnels dug into the face of a cliff, and produced by gravity drainage.
  The petroleum fly (Helaeomyia petrolei) is a species of fly that was first described from the La Brea Tar Pits and is found at other California seeps as well. It is highly unusual among insects for its tolerance of crude oil; larvae of this fly live within petroleum seeps where they feed on insects and other arthropods that die after becoming trapped in the oil.
caption: Oil Seep in the Simi Valley area of Ventura County, CA
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