During summer and fall the ground is bursting with thirst. During extreme dryness, the soil, even where there were marshlands before, develops this hexagonal crack pattern. There must be some theory in physics to explain the formation of this relatively stable pattern. The lack of moisture is so extreme that even after the ground is flooded with rainwater in late fall and winter, it takes some time before the hexagonal imprint of thirst softens. See the following images for comparison: this, this and this.