Most of a hoodoo is soft sandstone. In this soft sandstone, there may be layers (formed as sand was laid on an ancient beach and holes (formed as ironstones fell out). On the top of the hoodoo, there is usually a caprock (like on the left of the trio here). Caprocks are made up of many small layers and they are very hard. Caprocks protect the soft sandstone underneath from erosion. When there is no caprock, the soft sandstone erodes away very quickly, like for the two other pilars here...
Superb picture Rick. I have to tilt my head a little for the horizon but...this is a cool image.
