"Climate change doesn't happen overnight, nor is it a smooth process. The Painted Hills contain a record of both long-term climate change as well as the fluctuations that occurred along the way. For instance, those iron-red bands you see in the hills represent a warm and moist environment where the soil was usually damp. Ponds and lakes would have dotted the area. Rainfall would have been at least 31 inches (800 mm) per year, and may have been as high as 53 inches (1,350 mm) per year. The yellow and tan soils indicate a drier environment than the red layers, where standing water would not have been present in much of the area. Rainfall would have been between 23 inches (600mm) and 47 inches (1,200 mm) per year. Today's rainfall averages 12 inches. The black spots you see are caused by manganese concentrations. These are thought to be indicators of some sort of plant that fixed manganese in the soil, much in the same way that the Kenyan toothpick tree (Dobera glabra) does today."