Welcome to OB. I'm in Spartanburg as well. I'm the fool rolling around in the crazy looking Subaru wagon. Horsepasture is actually a further drag out than Old NC 105 which are both beginner level runs. From the western side of Spartanburg (I see in your tag thing in your profile that you are on the Gaffney side - I'm close to Cowpens), Horsepasture is like 2½ hours away. I would suggest exploring the Wilson Creek area as a starting point. There are some great tracks up that way with plenty of water. Specifically in that area, nice easy hard tracks are Globe/SR 1362, Edgemont/FS 45, Pineola/FS 464 & Maple Sally/FS 187. You can step up your challenges in that same area with Old House Gap or Brown Mountain OHV or if you want to go for the distance you can start linking them together.
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@Pathkiller Trailhawk said, the SCAR is gaining some traction but is still just a really rough patchwork. I did the TAT a few years ago, but I did it on two wheels instead of 4 - it has some tough spots for bigger vehicles. My most recent long run was the Georgia Traverse, it was a long haul to complete it. I think we had a little over 20 hours behind the wheel over 3 days to get all the way to the end and then it was a 7-hour drive home from Alabama. It can easily be done in sections though. Of the 390 total miles, only about 58% of it is unpaved so there are a lot of jumping on or off points.