Oil extraction is still big business in the Southland, but today locating signs of the industry can require a careful eye. Wells hide in plain sight as office buildings or masquerade offshore as tropical islands. In the back of the Beverly Center shopping mall, one quietly sips from the earth behind a nondescript wall.

But the wells were not always so clandestine.

Through much of the 20th century, oil derricks towered over homes, schools, golf courses, and even orange groves across the Los Angeles Basin, once among the nation's top-oil producing regions. Beginning in 1892, when Edward L. Doheny and his associates opened the region's first free-flowing well, each new strike would quickly attract a cluster of the wooden structures, which supported the drills that bored deep into the Southland's sedimentary strata.

One such thicket rose atop previously barren Signal Hill in 1921. Workers at a Shell Oil drilling site had hit a gusher that sprayed dark, crude oil more than 100 feet into the air. Because the surrounding land had recently been subdivided for a residential development, would-be homeowners elected to build oil wells on their tiny parcels instead of houses, creating a dense forest of wooden derricks.

Landscapes across the Los Angeles Basin witnessed similar overnight transformations as oil companies jockeyed to drain the region's rich petroleum fields, deposited tens of millions of years ago on what was once a sea floor and then buried under thousands of feet of accumulated sediments.

But perhaps nowhere was the change as striking as at the region's beaches, where the industrial landscape of oil extraction encroached on the Southland's carefully crafted image of perpetual summer. In Orange County's Huntington Beach, political concerns kept the wells on the land, where they formed a sort of palisade along the shore. And just east of Santa Barbara at the evocatively named Summerland beach, piers stacked with oil derricks stretched into the Pacific, standing firm against the crashing surf.

A cluster of oil wells near the site of Edward L. Doheny's oil strike, which set off the region's oil boom.Courtesy of the USC Libraries - California Historical Society Collection.

Oil wells on the beach in Summerland, just east of Santa Barbara, circa 1901-03.Courtesy of the USC Libraries - California Historical Society Collection.

Aerial view of Signal Hill and its artificial forest. Courtesy of the Herald-Examiner Collection – Los Angeles Public Library.

Circa 1926 postcard of Signal Hill. Courtesy of the Werner Von Boltenstern Postcard Collection,Department of Archives and Special Collections, Loyola Marymount University Library.

Circa 1941 postcard of the Signal Hill oil field. Courtesy of the Werner Von BoltensternPostcard Collection, Loyola Marymount University Library.

Two big Southland industries, citriculture and oil extraction, meet in Montebello , 1926.Courtesy of the Herald-Examiner Collection - Los Angeles Public Library.

Driving through a forest of derricks in Signal Hill. Circa 1937 photo by Herman Schultheis ,courtesy of the Photo Collection - Los Angeles Public Library.

An oil well once stood in the middle of La Cienega Boulvevard . Courtesy of the USC Libraries -California Historical Society Collection.

Oil wells in Huntington Beach, 1935. Courtesy of the Frasher Foto Postcard Collection, Pomona Public Library.,

Oil wells along Huntington Beach in the 1930s or '40s. Courtesy of the Orange County Archives.

Beachgoers frolic beneath the gaze of oil derricks in Venice. Courtesy of the USC Libraries -California Historical Society Collection.

Oil derricks made for unusual hazards at the Alta Vista Golf Course in Placentia in 1961.Courtesy of the Orange County Archives.

Island White, an artificial island in Long Beach Harbor, hides an oil well.1986 photo courtesy of the Los Angeles Times Photographic Archive,Department of Special Collections, Charles E. Young Research Library, UCLA.

This post was first published on KCET.org on August 11, 2011, as "Photos: How Oil Wells Once Dominated Southern California's Landscape." An expanded and updated version was subsequently published on August 6, 2015, and a different version was published on Gizmodo's Southland in November 2013.