A few things...First, those rocks stacked like that...That could very well be a marker to a cache! Make sure you hunt in all metal or in discriminate without any discrimination being turned up to you'll hear iron and dig any largish signals, even iron ones. Like say can size or bigger. If it's coins in a metal box you'll only hear an iron signal and not the coins. Second, make sure you not only hunt over those stacked rocks, but all around that area, because they might have used that only as a spot to pace off from to where they buried their loot. Also, if there any other permament markers around such as a very old tree make sure you check around that, because the rocks might have been just a secondary marker in case perhaps the tree they buried the cache by dissapears due to logging or something. You need to grid the whole area in a good radius around those stones, because they could have buried a cache anywhere and used those stones as a pace off marker. Either way, even if those stones were not used to mark a cache they are good spots for somebody to sit and rest and lose a coin out of their pocket. I always hunt around big bolders or anything people could sit on in the woods for that reason, let alone them being used to mark a cache. Even hunters will sit on stuff to watch for game quietly.
Next, that wall...Looks great! What it was for? Don't know. Looks too long to serve as a wall for a lean-to type cabin build I think, but you never know. For sure it took people and man power to build a wall like that, so even if they didn't live there there might be coins around. Especially coins paid to laborers to build the wall. Often guys would gamble at their worksite and also camp right there, so be sure to look for any ideal camping sites. Usually near water or on raised ground should it rain so that their tent's floors wouldn't get wet. Even a foot of elevation is what a smart camper will set up camp on to avoid the ground getting swampy where their tent was thrown. First rule of camping back in the day- Near water to bath, drink, cook, wash clothes, and water their horses. Second rule- Pitch your tent on higher ground, even if it's only a foot higher than the rest of the ground around it.
Third...That wall again...Be sure you also hunt in all metal or no discrimination in discriminate mode and scan the wall it's self. Often a cache was stuck behind a loose rock, so be on the look out for that too. Scan that wall top to bottom and if you get any kind of signal, even iron, be sure to pry out the stones there with a crowbar or something to see what is causing that signal. Stone walls were ideal for hiding caches.
Fourth...How did they get there? Is the terrain steep with only one way in and out? Remember they were probably riding horses too, so even a small sloping slope to get across a steep ravine or hill would be the way they went. I've found many coins at spots where that was the only way up and over a ridge spine for instance. And, if you do have ridge spines around there, often hunters and people riding horses would travel the tops of those spines as highways. That way they could keep their bearings, watch for unfriendlies below, and also it was a good vantage point to track and shoot game from.
Good luck and you BETTER let us know how it goes when you get a detector! Make sure to respond under the same post so we know to look for you when you do!
