While I know we rode but a small taste of this place in just a few days, we think we got a good feel for the desert riding of Texas. For advice we relied on Jean-Philippe back at College Station so long ago, and Desert Sports near Terlingua. Both mentioned the “warmup” trails East of the park entrance. The Lajitas Golf resort and Spa has created a very nice network near the airport there! (a very private, small and empty airport at that…not a single plane was seen or heard in the three days we were there)
The Lajita trails includes loops, stacked loops and bailouts to allow a taste of any size without forcing a poison dose upon the rider. The surface was hard, dry and packed enough to roll fast. 
Parts were tiny fractured flat rock bits that Jane deemed riding on Scrabble tiles. 
The 18″ wide curvy single track could have been weaved anywhere between the tough, scrappy, low desert growths. But knowing how fragile the desert is, nearly everyone stays right on the trail. We blasted about up and down what was probably only 1 or 200′ of rise and fall, making for flowy fun, fun, fun!!!
The flora is surprisingly diverse. My favorite is Ocotilla, a thicket-like bush that seems to grow everywhere, but favor those ridge lines where you might expect Indians to rise and run down over the plain. Fences and Ramadas are often made of this nasty, thorny stalk and Jane noticed some of the fences coming back to life. The hardy stalk seems to need little moisture and in place, wired into a structure starts to sprout if it touches the ground! Wow! Desert life surprises constantly. We saw a few different tiny and intricate flowers thriving inches from the trail too. I couldn’t help but share my Camelbak water during my rest stops…bet they bloom again next week. Kinda like those little shrunken sponge toys that grow to ten times their size.
The next day we thought we’d head for the Contrabando (yes, like contraband, or smugglers goods) Trails System. I wanted to ride in from the West gate, ride around the Contrabando Dome and back out. We wondered a bit why not many cars parked there. an early start led us into gravelly, then rocky, then sandy washes or draws. As we headed further in without the gleeful paybacks of sinewy buff trail, we contemplated where this was leading. we gave it another half hour before turning back. We “threw” the bikes quickly into the 4Runner sans Tramper, and drove hastily to the East Trailhead.
Two or three parked trucks confirmed what we’d been seeing this week. this is where riders start. Right off onto the Dog Cholla Trail, we weaved along terraces and tumbled through a few washes. The ratio was better though, we got what we came for! And More! The Crystal Trail was sparkling and spectacular! 
Again, bench cut joy riding around and up the shoulders of those spotty green-grey hills. It was so weird that one of them was COVERED IN CRYSTALS. And so hard NOT to pick one up as a souvenir.
We are so blessed to be riding this stuff. It seemed petty to bail out on that first ride….But it sure paid off!
-David
The Voyage of the Tramper 
Oh, that is just so cool!! I am curious as to why you didn’t grab some crystals as a souvenir? Against the rules for using the trail, or some other reason?
You are right – current practice is to never take any pieces or parts from State or National Parks. The Contrabando trails are in Big Bend Ranch State Park. It’s actually now illegal to take any natural souvenirs, including rocks. This has changed in my lifetime – or, at least, my awareness of the rules has changed! Now, we take nothing and leave nothing… even in non-Park settings.
Jane & David