Later, more strata were deposited. These comprise the Brule Formation. This is the major unit in Badlands Park. A dendritic network is a network of channels in which numerous tributaries join to define a pattern that looks like the veins on a maple leaf. This is the case in Badlands National Park because the expansion and shrinkage of bentonite weakens the rocks so it basically is just like weak clay.
Erosion occurs during sudden, heavy rains which cause a lot of erosion.
Then, the land dries out again. This is because of subduction of Pacific Ocean floor beneath North America. Magma rose into the crust and filled a magma chamber underground. Some magma rose to the ground surface and erupted to form volcanoes. Some of the magma froze inside or just below the volcano.