Are you bringing your own horse, or looking for a place that "rents" trail horses?
There's a big difference - a lot of places, even those that will rent out a trail horse and let you go out on your own, may require you to go on some guided rides first so they can tell that you are competent enough to go out on your own and will not get yourself or the horse hurt. They also want to be sure they're not about to let someone take one of their horses out on trail and run it into the ground.
Not suggesting you would do such a thing. . .but sadly, there are people who would.
A lot of people show up even at guided trail barns, puff out their chests and call themselves "experienced riders," then it turns out they don't know one end of a horse from the other.
If you're just looking for places to ride your own horse, there are a number of horse trail directories online, such as www.horsetraildirectory.com
, that provide descriptions of the different campgrounds and trails, the terrain, etc.