Sweet! Fine trip, fine photography! Thanks for posting.
The vehicular contraption identified as a hay stacker is a buckrake. The task of the buckrake operator is to scoot along a flat-lying hay meadow windrow of cut, raked, and sun-dried hay, fill the rake's L-shaped bucket full by driving down the axis of the windrow, lift up the bucket a bit, and drive the load over to the beaverslide. At the beaverslide, several buckrake loads are accumulated on a slightly tilted L-shaped lift. When full, a buckrake or tractor backs away from the beaverslide, pulling a cable run through a pulley system which raises the tilted back lift up an inclined "slide" to the top of the 25-30' tall wall of the beaverslide. At the top, the lift catches a spur and flips backwards suddenly, dumping the load into the middle of the beaverslide, itself a home made tall, four-sided frame bound by wire and fencing. The fall compacts the hay on the bottom and subsequent lifts add height and more compaction. When full to the top, the beaverslide's dogwire sides and their support poles are disassembled and, along with the inclined ramp which the lift rides upon and the lift and cable system, is moved elsewhere in the hay meadow to build another stack. Given the way it was compacted, the haystack stands without further support.
The buckrakes are home-made and the subject of some pride among ranchers. Many have been in use for +50 years. Most are a 2WD truck chassis with the operator's seat facing rearward such that the steering is in the rear. The steering, accelerator, brake, and clutch pedals and the manual linkages are all re-designed and run to provide for the rearward-facing primary operation. The buckrake bucket and its lift mechanism face rearward right in front of the operator.
In Montana's Big Hole, the Hirschey family brings in some of their single annual cutting of hay by the beaverslide/buckrake method, and in recent years has done so with an all-female crew. The matriarch runs the same buckrake, built by her father, which she was trained on as a young girl. Back in the day, it was commonplace to see children running their ranch's buckrakes.
There are some cool YouTube videos of buckraking in the Big Hole, including some of the Hirscheys.
Foy