I was going to ask what you mean by trail riding, but someone beat me to it. You are certainly poised in the right area of CA to find a good trail horse! Being so close to Tevis country and the foothills, there are TONS of trail riders up there - both people who do endurance and people who “just” trail ride (even though trail riding could be camping, going down single track on the side of a hill, going over bridges, through rivers, etc.).
I don’t know if you can do ISO ads, but you might check with some trail clubs around the foothills areas. I have a couple friends who are in this club: http://www.goldcountrytrailscouncil.org/.
If you are open to mustangs I could see if the guy I got mine from is still working with them. Last I heard he was interested in doing Tevis, but he used to get mustangs and burros from the BLM and train them up and take them out on packing (hunting) trips, so they’ve seen everything (although green under saddle for what you’d be used to with a green w,t,c dressage horse) and will go anywhere. Mine is an AMAZING trail horse (but like I said, was very very green about any sort of “refined” riding and doing any sort of arena work). I would take him anywhere and feel confident that he could handle the situation (and since I got him did “dressage” him up;) to get him more rideable).
Good thing about mustangs is that most of them are so hardy as to not need shoes. They are small enough to get off/on while out riding, or duck under tree branches or whatever. They are very careful with their feet.
I would not sell my mustang for anything. His trustworthiness and the miles and experience I’ve put into him make him priceless to me. That might be the thing with finding a good trail horse to buy. Just like anything, the really good ones aren’t sold.
If you’re open to QH, you might check with Bryan Neubert. I don’t know what his horses go for, but he breeds (and starts) his own and they get a thorough education going out on his ranch. I have a friend who has one of his horses and he’s an awesome horse. Great brain, sound, solid horse.