I think we’re still in Custer State Park, and I’m not going guess at the process that formed these distinct rock towers – oh, hell, yes I am. It’s likely layers of a harder stone, formerly sedimentary, that got uplifted by geologic folding and then weathered away. But that’s not important (sorry geologists.) More useful to us – since you’re on a nature photography site – is the way the light works. Textures like these beg for sharp and distinct sidelighting, which emphasizes their coarse nature. Direct light, such as immediately behind the camera, wouldn’t make these half as forbidding. High contrast light can have a negative effect on many kinds of photos, but it’s situations like this where it works very well, throwing all of those edges into sharp relief. And the framing with the tree layers really kicks it, too, providing a lot of depth to the scene while mimicking the rock formations. I like it.