So here is the site of the outdoor set where they did the exterior scenes for both the M*A*S*H movie and TV show.
This mountain was in the backdrop of many scenes in the show:
See? (Internet screen capture from M*A*S*H movie opening credits):
This is a replica of the signpost:
This is one of the ambulances from the show.
It would have looked like this back in the day (Internet screen capture from M*A*S*H movie opening credits):
Here's one of the jeeps:
This is looking down on the tent site from the helicopter pad. If you enlarge the photo, they have the site of some of the tents marked out with rope behind the ambulance. The dip in the foreground would be around where the steps were that Hawkeye and company used to run up to meet the incoming wounded:
This is the helicopter landing pad, taken from above it. The road the ambulances took is out of the photo to the left. It's still there, but couldn't get a photo of it due to it being in the shadow.
Here's an aerial shot of the area from the opening movie credits 40 years ago:
This is the path up to the helicopter pad from the camp. It was backlit so it's a crummy photo.