The second fire road off the Panoramic Highway!
Hank and Hope set up the lab in a secluded portion of Muir Woods. In reality this scene was filmed in a field near the Pinewood Atlanta studio, and used digital effects to make it look like Northern California.
According to Cinefex #160 the scenes in the Muir Woods clearing were filmed just outside the Pinewood Atlanta facility.
(Ant-Man & The Wasp, 2018)