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   The 4077th actually consisted of two separate sets. An outdoor set in the mountains near Malibu, California (Calabasas, Los Angeles County, California) was used for most exterior and tent scenes for every season. This is the same set used to shoot the movie. The indoor set, on a sound stage at Fox Studios in Century City, was used for the indoor scenes for the run of the series. Later, after the indoor set was renovated to permit many of the "outdoor" scenes to be filmed there, both sets were used for exterior shooting as script requirements dictated (e.g., night scenes were far easier to film on the sound stage, but scenes at the chopper pad required using the ranch).

Everything you want to know about M*A*S*H here> http://en.wikipedia.org/wiki/M*A*S*H_%28TV_series%29

Just as the series was wrapping production, a major brush fire destroyed most of the outdoor set on October 9, 1982. The fire was written into the final episode as a forest fire caused by enemy incendiary bombs.

The Malibu location is today known as Malibu Creek State Park. Formerly called the Century Ranch and owned by 20th Century Fox Studios until the 1980s, the site today is returning to a natural state, and is marked by a rusted Jeep and an ambulance used in the show. Through the 1990s, the area was occasionally used for television commercial production; for example, a Miller Beer ad with a "Mexican" setting was filmed there.

On February 23, 2008, series stars Mike Farrell, Loretta Swit and William Christopher (along with producers Gene Reynolds and Burt Metcalfe and prolific M*A*S*H director Charles S. Dubin) reunited at the set to celebrate its partial restoration. The rebuilt iconic signpost is now displayed on weekends, along with tent markers and maps and photos of the set. The state park is open to the public. It was also the location where the film How Green Was My Valley (1941) and the Planet of the Apes television series (1974) were filmed, among other productions.

When M*A*S*H was filming its last episode, the producers were contacted by the Smithsonian Institution, which asked to be given a part of the set. The producers quickly agreed and sent the tent, signposts, and contents of "The Swamp", which was home to Hawkeye, Trapper, Frank, Spearchucker, BJ and Charles during the course of the show.[17] Originally found on the Ranch, Radar's teddy bear, once housed at the Smithsonian, was sold at auction on July 29, 2005 for $11,800.

The indoor scenes were filimed on sound stage at 20th century Fox Studios in Century City. Los Angeles. Calofornia. Out door set used  for the movie in early years is now part of Malibu Creek State Park.