Back in the day at Fort Campbell, we worked through three cycles, each denoted by a different color. As there were three brigades within the division at the time, one brigade would be in a different cycle at the same time. Each cycle usually lasted about 6 weeks or so.
One cycle would be a training cycle, when we'd be in the field-whether it was the Back 40 on post, JRTC at Fort Polk, or up at Fort Knox. The major focus was building from squad/section level up to brigade level operations.
Another cycle was spent as the Division ready brigade. During that time, we were the first ones who would get the call to deploy, should the SHTF. We were on a 2-4 hour recall, passes were limited in number and scope, and our day-to-day work involved training around unit area. Our vehicles and connexes were loaded, weighed, and stored in a secure site near the airfield, so that we could be ready to load onto aircraft as soon as they began arriving. (My brigade was in the midst of this cycle when 9/11 occurred.)
The third cycle was for post support and block leave. During that cycle, we were given the opportunity to take a couple weeks leave, if we had any saved up. It was also the time to enroll in college classes. If you weren't on leave or in class, you were available for post support tasks. (And those taking classes were usually only excused from post support taskings if they had reenlisted and gotten the commander to agree to let them have time off for school.) Post support tasks could include a wide range of details. They included, but weren't limited to, funeral details, police call / litter pick up around post, working the desk at the post museum, providing an NCO for the GuardFIST (where we artillery guys practiced and taught call for fire on a projection screen), supporting Range Control, and even sending soldiers out to work at the place which sold hunting and fishing licenses for on post.
It sounds like your son might be in the middle of a similar cycle and happens to be the Joe tasked with working at the Rod and Gun Club facility or something.