Leaving Norman and going East on Highway 9 takes you past the USPS training facility, a Hitachi plant, ranches and pastures and 15 miles later you arrive at the entrance of the
Lake Thunderbird State Park. There are two entrances: one takes you to Thunderbird Stables, camping grounds, and the boat dock; the next entrance further East from Norman on HW 9 takes you to the dam (so you can see the whole dam thing).
From both locations, you can get to the park's
mountain bike trail system.
There are five trails - two entry level trails, two medium, and one advanced (the Gold Loop).
You access the "easy" trails from the first park entrance; the trail heads are right across the road from the stables. You start on the Green Loop and then continue on the Yellow; coming back to Green and back to the trail head, for a combined trip of 2.5 miles. It is a nice ride; gentle curves, no sudden drops, gentle slopes, and no treacherous trees and rocks blocking the trail. Yet it is not a piece-of-cake ride - there are some drops, turns with sand traps, ups and downs that wear you out if you are not used to biking and test your bike's rigidity. There is a sign at the trail head requiring riders to wear helmets; it is not a joke, but a very sensible proposition - even if you are only going to stay on the two easy trails.
If easy is too easy, try the two medium trails - Red and Blue. You can get on Red from the easy Yellow; do Red and Blue and then loop back on Yellow - this time bagging a respectably long 6.5 mile ride. I am a bad biker and I can do this trip in about 50 minutes. These two intermediate loops are far more difficult - both physically and technically. Sharp turns, steep climbs, sudden drops, rocks on the path - or all of the above at once, generously sprinkled all along both trails. I can't ride them without getting thrown off the bike at least twice, hitting a tree with my helmet a couple of times or rubbing it with my sleeve - or if I am lucky, even flying over the handlebars.
If that's still not enough, there is the advanced Gold Loop. Again, you can access it from the middle of Blue, do it, and then come back to Blue - this time doing all five trails; or you can access it from another park entrance, the one next to the dam, and do just the Gold. Do not do it unless you can do the other four with ease. It is by far the most challenging of the five; downright dangerous if you don't have enough skill. Don't take your Walmart bike there unless you are suicidal.
The Gold Loop makes a perfect trail run; access it from the dam entrance, adjust the length by doing all of it or taking an occasional bypass on some of the twists.
Last time I rode the first four trails, I saw three deer, a skunk, and no humans on the trail. It is an excellent way to get out of Norman - get your adrenaline going, exercise, socialize with skunks and deer, look at the water, glimpse at the horses, dip your feet in the lake, look at the sunset, and head back to Norman - which is only 15 miles away.