Click for detail: Fake Town | Fake Airport | Driving Range | Performance Range | Underground Storage | Obstacle Course | Black SUV
The fake town and fake airport are for "real-life" exercises involving urban and airport situations. You can see that there is a simulated half of Air Force One, but not the whole airframe. I've seen a television program where agents were shown practicing various security activities (VIP arriving by airport, bombing in an urban environment).
The driving test range appears to have different kinds of paved street configurations, presumably for practice cornering and turning. The "performance" range, as I called it, is probably for high performance manuevering practice, like "J-turns" (you can even see the turn guide lines painted on the tarmac). It also appears to have a heli-pad.
I'm guessing that point E is some kind of underground storage, perhaps for munitions (especially considering the Jersey barriers obstructing the entrance). The obstacle course is not so obvious, but it's easier to see on Microsoft's Live Map of the location, and it contains a bunch of different swings, pits and balancing obstacles. It looks challenging!
Finally of course, the Black SUV (or maybe it's a van on the day this photo was taken) is present near the intersections of Soil Conservation Road and Powdermill Road.
There are probably other Easter Eggs to find, it just takes some diligent scanning. For example, the old Beltsville Agricultural Center airport is just to the southeast, and I believe the Secret Service uses that for training as well.
By the way, none of this is particularly secret. All these maps and satellite photos are available to the public via Google Maps, and several of the locations listed above were showcased on a recent Sixty Minutes story about the Secret Service.
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