A brief lesson on horse shoes. First -- the above picture that is attempting to date horse shoes. All those style of shoes are being used today. Any horse shoer that does corrective work, and makes hand made shoes will make shoes that resemble the ones pictured. The best way to date a horse shoe is what else did you find in the area that is date-able.
The hoof wall of a horses foot will grow an average of 3/8's inch a month. Wild horses will wear their feet off at about that rate, however horses kept on nice soft pasture will need their feet trimmed to keep them from getting too long and breaking up. Horses being ridden or driven will be forced to wear their feet down at a faster rate than they grow, and their feet get tender and the horse goes lame. The answer to that is to put iron shoes on the animal. When the horse or mule is shod, the hoof wall is trimmed back and the foot leveled, the shoe is shaped to fit the foot and nailed on. Now the hoof wall is protected and is going to grow 3/8's inch per month. If the foot is allowed to grow to long, there are a number of things that can go wrong, which I won't go into, but worse case, the end result can end up with a lame horse. Therefore the Army required the cavalry horses be shod every six weeks. The horse would get new shoes, 6 weeks later the farrier would cut the clinches off the nails, and pull the shoe. He would then trim the excess hoof wall, and nail the same shoe back on, which is call "resetting the shoe." Then 6 weeks after the shoe has been reset, they are usually so worn and thin that those shoes are pulled and new ones put on. Now, just because the army did it that way doesn't mean everybody does it that way, and in fact most people don't. Shoeing a horse is expensive, and people tend to leave them on the horse as long as possible. Depending on the hardness of the ground, and the length of time the shoe is left on the foot, or if the shoe has been reset, an iron horse shoe can wear in two at the toe. In another life I packed animals and rented saddle horses into an area in the High Sierra Nevada called Desolation Valley. The trails had no dirt on them, the country was solid granite, and the horses got lots of miles. Many times the new shoes on the horse would wear in two in a month. One more thing, horses and mules have different shaped feet, the mule foot is narrower and the hoof wall straighter than a horse. Also, the front foot of a horse is shaped different than a back foot. There are many different shapes and styles of horse shoes, and different traction devices used, that I'm not going to get into, it's just to much. Different shoes are used to correct certain things about the way the horse travels, or help heal an injured foot, or for traction on ice or in mud or when pulling a heavy load. I'll include a couple of pictures to show the difference shape of the front, back and mule feet.

The shape of the front foot.

The shape of the hind foot, and a mule shoe for comparison.