This is the down-range section of the base, an extremely high security area. Even authorized soldiers known to military police guarding the site would be held at gunpoint if they were found in a part of the site they were not expected in. This sign is a replica of one originally placed outside the fence you just came through, and it is an example of the kind of security expected here. 

The sign’s text reads, in English and Spanish:U.S. ARMY
RESTRICTED AREA
USE OF DEADLY FORCE IS AUTHORIZED
WARNING
THIS SITE HAS BEEN DECLARED A RESTRICTED AREA BY AUTHORITY OF THE COMMANDING GENERAL IN ACCORDANCE WITH THE PROVISIONS OF THE DIRECTIVE ISSUED BY THE SECRETARY OF DEFENSE ON 20 AUGUST 1954, PURSUANT TO THE PROVISIONS OF SECTION 21, INTERNAL SECURITY ACT OF 1950. UNAUTHORIZED ENTRY IS PROHIBITED. ALL PERSONS AND VEHICLES ENTERING HEREON ARE LIABLE TO SEARCH. PHOTOGRAPHING, MAKING NOTES, DRAWINGS, MAPS, OR GRAPHIC REPRESENTATIONS OF THIS AREA OR ITS ACTIVITIES, IS PROHIBITED UNLESS SPECIFICALLY AUTHORIZED BY THE COMMANDING OFFICER. ANY SUCH MATERIAL FOUND IN THE POSSESSION OF UNAUTHORIZED PERSONS WILL BE CONFISCATED.