The "water collection drums" are microwave relay antennas that at one time were probably up on that or an older tower at the site.
https://www.rfsworld.com/ The radio compound is registered to the [county] Sheriff's Office and currently used as a public safety radio repeater & microwave relay site. Probably also some cellphone antennas on it too.
I don't think the wooden structure was ever some sort of ranger/fire lookout station. I believe it was purpose-built way-back when (possibly as early as the 1920s) as some sort of radio station. Older radio gear was quite big & bulky (compared to the modern radio equipment hut nearby), and if it was important enough, and/or very finicky, then sometimes a technician on-duty would stay at the location for their shift. For sites that didn't need a technician there always/frequently, because many radio transmitting stations were located on remote hill or mountain tops, there was always a risk that a technician/caretaker could be stuck there during bad weather, so this was another reason the older radio sites may have some sort of living space (bathroom, kitchen, bed area...) in it as well as the spaces housing the radio gear, spare parts, a work bench, generator, etc.
I do get what you mean about the ground level interior kind of looking like a horse stable. Some radio towers and equipment buildings are owned by one person or company, who then leases building and tower space to a variety of others needing radio -- a taxi company, local fire department, etc. and a lot of the interiors of the buildings would have separate, secured space for each renter. That way if I was up there to fix my taxi company radio repeater, I couldn't poke-around with the gear belonging to someone else (stealing a fuse, just so I could get my system back ion the air, etc.).
The barn-style doors on the second floor would have been to get large, heavy equipment in or out. BUT of course if it did ever serve as a barn, the doors could have been used to get bales of hay into the hayloft... But it looks like kind of a strange place for a horse or livestock barn, great site for a radio facility, now & throughout the past.
/-/ooligan