Welcome from Stillwater! We have lots of nice trail riding in this state and quite a bit of it is an easy drive from OKC, you should meet lots of nice folks out there. Check out Bell Cow Lake near Chandler it's gorgeous, Prague Lake is neat too, they have all kinds of trail obstacles set up along side the trails and you can practice on them or not as you choose, and Lake Carl Blackwell is a personal favorite with over 26 miles of varying terrain and trails of all levels. All 3 of those rides are within 1.5 hrs from the OKC area.
GO 'POKES! Big 12 Conference Champs!