Thank you so much Olttoot for your reply. I'm slowly piecing this together.
You are absolutely right about the usage. In cleaning it, it was obvious that the horse beneath it worked very hard through mud and manure (as it and sweat were embedded in the stirrups and fenders), and then the saddle fell into ignorant hands and was neglected.
I found a Ray Holes saddle made in 1963 that had the same rigging up front, (and just a leather slot in the rear) so I think you have the timeline right. The fellow who runs Cowboy Showcase thinks the saddle is production made, otherwise it would have a name on it, but if the maker's marks are sometimes stamped on the latigo keeper, I could see how that could be broken off over time - unfortunately. He definitely thought it originated from the southwestern United States, but I won't rule out Dixieland if you think there's a trail there. I'm in New York, so there's no question the saddle has traveled far from home.
It wasn't me who labeled it high quality, it was my saddler, Dick Jolley, who is 84, been working with saddles for over 40 years, and specifically said how impressed he was with it and even wants to use it to train his two apprentices because the workmanship is so rare and excellent. He's offered to write a letter of recommendation attesting to its quality. The tree is wooden, sound and wrapped with both canvas and rawhide. The leather is extremely thick and now that it has been cleaned, beautiful - very deep and lustrous. (And oh boy, does Mr. Jolley like that elephant ear cantle!) The saddle seat is padded and soft. Steel rod in the stirrups, heavyweight blevins buckles. Mr Jolley said that back when the saddle was made, the border with Mexico was very porous and that frequently, Mexicans came into New Mexico to work on saddles. He said they were some of the most clever saddle makers - at least to his taste - at the time (he also thinks 60's) and might have had a hand in this saddle.
It's a fun little history project and making me fall in love with saddles and leatherwork, that's for sure. Thank you for contributing to it.