According to MASH4077TV.com., episodes of MASH was filmed in two different locations. The external shots were filmed at what is now known as the Malibu Creek State Park. At the time it was the Fox Ranch located in the Santa Monica Mountains in California. Fox donated the Ranch to the state of California while MAS*H was still in production. The fire that engulfed the 4077th in the final episode was an actual wildfire that was worked into the script.
The internal shots, such as those taking place inside the Swamp or the O.R. were filmed in Stage 9 of the 20th Century Fox Studios in Hollywood, California. Limited shots outside the 4077th were also shot inside Stage 9, mostly the area between the various tents and buildings.
MASH is a television series created by Larry Gelbart. It was inspired by the 1970 Robert Altman film of the same name.
The series premiered Sept. 17, 1972, and followed the staff of a hospital in South Korea during the Korean War. Its stars included Alan Alda, Loretta Swit, McLean Stevenson, Jamie Farr, Wayne Rogers and Harry Morgan.
See full cast and crew at IMDb.
Check out 17 Painless Facts About 'MASH' compiled by Mental Floss.