A hoodoo is a column of rock which typically forms within sedimentary rock or volcanic rock formations. The cap on top of a hoodoo is generally formed because it is made from harder rock that erodes at a slower rate than that of the hoodoo.
Hoodoos generally form in arid desert conditions or in badlands such as the Bisti Wilderness area in New Mexico, USA.
In this picture of a hoodoo and cap rock, the sandstone is caught in the beautiful golden light in the late afternoon in the Bisti Badlands.
Bisti/De Na Zin Wilderness, New Mexico, USA