The Sawbuck Pack Saddle has ancient origins. It has been in regular use since the time of Genghis Khan. Its design is simple and variations, such as the camel saddle of the Middle East, appear worldwide. As the pack saddle of the fur trapper and the prospector, the sawbuck pack saddle played a role in opening the American west. In the years following the Lewis and Clark expedition, sawbuck pack saddles packed just about everything a horse could carry. Joe Back, in his book "Horses, Hitches and Rocky Trails" had this to say about the Sawbuck pack sadddle:
The Sawbuck pack saddle is most like the one the Indians devised; it has wooden cross-pieces front and back (where the Indians used deer or elk horns) and carved wooden side bars. Just because one of these resembles in construction that old woodcutter's pride, the sawbuck, doesn't mean it has both uses. I believe that of all the kinds and types of pack saddles used in this country and Canada, you'll find more of that good old standby, the sawbuck, used than any other. There are many advantages, and, some say, improvements in some of the others. But that old sawbuck, well-constructed, with good, well-shaped bars and wide enough in buck construction for average animals, is just hard to beat for general packing. When it's rigged evenly and accurately, using high quality leather, with snaps, rings and buckles that can be adjusted to suit the build of the particular animal, with comfortable cinchas, you can move a lot of cargo.
The first Decker Pack Saddle tree of its kind (with wooden bars and steel bows) was first used by an Arapajo packer named S.C. MacDaniels in central Idaho during the mining boom of 1898-1900. Several brothers named Decker saw the practicality of the idea, adopted it and made improvements to the Arapajo cover, or "half-breed" as it is know today. They applied for a patent on the tree and rigging, which apparently was never granted, and the name Decker Pack Saddle stuck. In the early 1900s, the Decker brothers established themselves as some of the finest packers in Idaho and Montana, packing thousands of pounds of equipment and supplies into the unroaded, trail-less terrain of the Selway and Lochsa Rivers, over Lolo Pass and into the Bitterroot Valley of Montana. All the while they were demonstrating the durability and versatility, as well as humane nature, of the Decker Pack Saddle.
The modern Decker Pack Saddle tree was perfected by blacksmith/saddle maker, Oliver P. Robinette of Kooskia, Idaho shortly after 1906. Robinette is credited with developing and manufacturing hundreds of the Decker trees and pack saddles for the Decker brothers as well as for local sheepmen and other outfitters and packers of the era. The Decker brothers could foresee a rapid increase in the use of this unique and clearly superior pack saddle and they made a deal with Robinette to market the saddle. It was advertised and sold as the Decker Pack Saddle. In later years, O.P. Robinette built many trees for the Forest Service (the "OPR" style Decker Pack Saddle tree) until his death in 1945.
At that time – the twilight of the old west – a generation of packers skilled in the use of the sawbuck and the traditional diamond hitch were passing into history, while a rapidly growing Forest Service needed transport for heavy, often bulky equipment through the vast roadless back-country. The Decker Pack Saddle, a rugged versatile saddle that could be easily packed to capacity by Forest Service personnel, filled this need. It caught on quickly throughout Idaho, Montana, Oregon and Washington, while in Wyoming, Colorado and California packers continued to use the sawbuck. In 1930, a "Remount Depot" was established in the Ninemile Valley west of Missoula, Montana, as a place to raise and train horses and mules, as well as train packers for the Forest Service. Horses and mules in sufficient quantity to supply fire fighters duing critical fire seasons had become difficult, if not impossible, to obtain from private sources. The Decker Pack Saddle was adopted as the official saddle and packing style in Region One (all of Montana, Northern Idaho, North Dakota and a bit of South Dakota). Part of the mission of the newly established Ninemile Remount Depot was to "develop improved methods of packing and standardize packing practices." In 1937, a standard specification for the Decker Pack Saddle was prepared and that specification, with only minor modification, is still used today as the basic design of most Decker Pack Saddles.
The above information was taken from “Packin' In on Horses and Mules”, Elser and Brown, 1980, "The Packer's Field Manual", Hoverson, 2005 and "Horses, Hitches and Rocky Trails", Joe Back, 1959.