Lots of areas look like they've received heavy shelling or bombing, so I'm guessing it is an Army artillery practice range or an AF bombing range. Lots of the structures, planes and tracked vehicles could be used for aiming and identification practice for the airmen coming out of Mountain Home AFB.
Based on the description below, Saylor Creek may be getting a lot of use now.
Saylor Creek is a 110,000-acre bombing and training range in southern Idaho. It is associated with Mountain Home Air Force Base, located 25 miles north of the range, but is used by aircrews from other bases as well. The range is primarily used by flying forces training for air to ground warfare, and is covered with simulated hostile radar facilities, most of which are moveable electronic "threats," like those used on the Nellis Range in Nevada and elsewhere. Simulated surface to air missile batteries, employing "Smokey SAM" simulated rockets, are in use on the range. Visual targets, electronic warfare training, and live bombing are also components of the range's function. The Air Force has made numerous attempts to expand the range, efforts normally defeated by opposition from environmental groups and locals.