They go by many names in different places. While hoodoo is the most common name, they are also referred to as “fairy chimneys”, “sand mushrooms” or even, rather absurdly, “goblins”. They started with a layer of hard rock on top of a softer layer of sandstone below. This cap of rock is typically around 40% calcite cement, which holds up extremely well against the elements and is very slow to erode. So, while the vulnerable sandstone erodes at a relatively fast pace, the portion directly below the calcite is protected from the brunt of the rain, snow and sun.It takes hundreds of years for hoodoos to form through a repetitive process of freezing and melting, plus the constant effect of wind. Eventually you are left with a narrow chimney-shaped formation directly below the protective rock cap.