Hello,
I just stumbled on this thread, and I don't have time to read it entirely, sorry... so if the following is information that has already been made available, please ignore me.
Just wanted to say that I've recently been at that place. The area is brimming with military activity, there are helicopters flying, you can see tanks and heavy artillery etc. You can also hear artillery fire. The white numbers are targets, I've seen tanks taking shots at them.
The Chinese characters on the ground serve various purposes; some I couldn't read, some warn of the area being off-limits, some say "protect nature" *g* etc. Note that in China it's relatively common to write huge characters on the ground (usually white stones are used), by and large the meaning is rather basic and uninteresting (protect the grass, don't go here, in some years this will be a green garden and more such nonsense).
In the area, there are lots of military patrols. The soldiers are friendly and approchable, but don't give any information if you ask them.
As I said, I've got no idea whether the above is of any use to you guys.
Greetings