This is one of my favorite hikes in my favorite national park. The standing granite stones were formed when magma was forced up into cracks in higher rock levels, cooled forming these stones and then the surrounding rock eroded away, leaving these standing stones.
Walking through this valley you can understand why the Commanche creation story said that when the Great Spirit finished making the earth he placed all of his left over stones in the Big Bend region.
The balanced rock is, of course, a major photo opportunity.
Despite all the warnings about needing four-wheeled drive or a high clearance vehicle to get here, I once accessed the trailhead in a miata. Just make sure you drive slowly, very slowly.