in reserved areas along the beach

I may have an idea where “Mystery Girl” is from based on the number she gave Pearl, (301) 555-0189 (or (301) 555-0789, depending on which shot you look at).

In the real world, 301 is the area code not for Delmarva (the region Beach City is in), but for the western half of Maryland (the state which occupies most of the Delmarva Peninsula), including Maryland’s part of the DC metro area. However, 301 served as the area code for all of Maryland until 1990.

Beach City is canonically along Rehoboth Bay in Delaware, which in reality has area code 302, so what was shown is close, but not quite.

The show takes place on an alternate version of Earth, and we have seen time to time that the geography of Earth is different, both physically and politically. Therefore, Mystery Girl could be from the area that corresponds to western Maryland in our universe.

(Also of note, only 555-01xx is reserved for fictional use these days. The rest of the 555- prefixed numbers were released for public usage years ago due to the exhaustion of available phone numbers.)

White door in B&W: SFUSD Environmental Science Center. Fort Funston, 09-27-14.

From Wikipedia (For some strange reason the park’s official does not have anything about its history.)

Fort Funston is a former harbor defense installation located in the southwestern corner of San Francisco. Formerly known as the Lake Merced Military Reservation, the fort is now a protected area within the Golden Gate National Recreation Area (GGNRA). It was named in honor ofFrederick N. Funston (1865–1917), a General in the United States Army, and includes an artillery battery bearing his name. The fort is located on Skyline Boulevard at John Muir Drive, west of Lake Merced.

The Fort was constructed upon windswept headlands along the Pacific coast and Ocean Beach below, above steep sandstone cliffs that provide a nesting habitat for a colony of bank swallows (Riparia riparia). The last remnants of a sand dune ecosystem that once covered the western half of San Francisco grows along the top of the headlands, with trailheads forming part of the California Coastal Trail that runs through San Francisco County.[2]