West -- a perennial top contender that came in fourth last year -- won with a score of 44,592 points out of a possible 60,000.
Last year's winner, Keppel High School of Alhambra, finished a close second with 44,438 points.
By winning the contest, West automatically advances to the California Academic Decathlon March 13-16 in Sacramento.
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However, Keppel and six other county school teams -- Torrance (which won the Super Quiz), Alhambra, El Rancho of Pico Rivera, South High School of Torrance, Redondo Union and Beverly Hills -- also scored high enough to qualify as wild card entrants in the state contest.
The 2009 LACAD results were announced Thursday by Los Angeles County Superintendent of Schools Darline P. Robles during an award ceremony at the Quiet Cannon Country Club. A total of 66 teams and more than 600 students participated in the LACAD, including 16 squads in the Junior Division.
The competition, presented by the Los Angeles County Office of Education, took place Jan. 31 at El Rancho High School and Feb. 7 at USC.
The top-scoring individual decathlete was senior Anthony Wu of Keppel, who tallied 8,880 points out of a possible 10,000.
He was followed by Daniel Naphas, a senior from Torrance, who scored 8,570 points, and Keita De Carlo, a senior from Palos Verdes Peninsula High School, who ended up with 8,461 points.
Decathletes are tested in 10 subjects: art, economics, essay, interview, language and literature, math, music, social science, speech and the Super Quiz, which is also science.
The LACAD is open to public high schools outside of the Los Angeles Unified School District, which holds a separate Academic Decathlon competition and awards ceremony.
This year, the contest focused on the subject of Latin America.
The state winner earns a trip to the U.S. Academic Decathlon April 22-25 in Memphis, Tenn. Last year's state champ, Moorpark High School of Ventura County, is the defending national champion.