Rocky Hill Ranch out in Smithville (East of Bastrop) has a couple of fun downhill sections, albeit, not miles of downhill, just bursts.
I think you’ll be hard pressed to find a legit DH trail.
I frequent Walnut Creek, in my opinion, one of the better all around trails. Has some climbing, some technical, some cruising, plus it’s right next to my house. 😀
Brushy Creek, bleh. I need to go out there with someone who knows where to go, when I went there it seemed like we took the most uphill/technical path and it sucked.
Barton Creek is OK, pretty flat unless you go uphill on Sweet 16. I don’t like climbing all day, but I do like to get some sort of work-out, don’t think I ever lost my breath in a couple rides out there. Again, riding with someone who knows the trail would probably make me eat my words.
Welcome to Austin!