Patterns of horizontal and vertical cracking form naturally geometric art. The sun-dried field of clay was deposited during the calming of a water-mud slurry that had cascaded from nearby erosive badlands. The smooth-sided, basically rectilinear pattern to the cracks indicates a young deposit--likely just one or two generations of drying since the creation of the sediment. Here's the wide landscape context for a rather stark view of the setting.
2 NE Interior SD (16 Jun 12) Looking down