As my original post for Halloween: H20 was over 1600 pictures and took a long time to load, I decided to split it up into separate scenes to make it easier and quicker for pictures to load:
Back in 2013, I found the rest stop area. It took me a while to track down this one, but my perseverance and patience paid off. The rest stop entrance is the drive into Malibu Creek State Park at 1925 Las Virgenes Road in Calabasas, California.
Now the actual restroom used is tricky. There are a few restrooms in the area of this park, but none quite match up the exact building nor position as seen in the film. It's possible that they have been moved or some set decoration changes were made. This restroom appears to be in the approximate spot based on the slope of the mountain and the highway seen in the background, but is not it - still leaving it here for reference.
There is one restroom that matches the doors and bricks. EDIT: This appears to be the one used in the film.
For the reverse shot, you can see how mountains line up in the background.
NEXT SCENE: Keri at school