From GolfDigest.com comes this description of the AT&T Oaks Course at TPC San Antonio.
Perhaps the most distinctive feature of the Oaks Course, current host of the Valero Texas Open on the PGA Tour, are not the thousands of squat live oaks which edge most holes, but the vertical limestone back edges of several bunkers, formed when those bunkers were literally chiseled or blasted from the subsurface rock. The walls of rock add distinctive beauty and a bit of intimidation factor. Luckily for golfers, most of the bunkers don't have a hard rock edge to them. That includes the bunker positioned in the middle of the green on the par-3 16th. It's intimidating in a whole different way.