Earth pillars. Earth pillars, or hoodoos, at the Writing on Stone Provincial Park, Alberta, Canada. These pillars are made of soft sedimentary rock and are topped by a layer of harder rock. They are formed due to the presence of large pieces of hard rock in semi-arid regions of sedimentary rock that experience occasional heavy downpours. The rain weathers away unprotected material leaving behind columns of rock under hard caps. Writing on Stone park is famous for its earth pillars and the carvings made in the rocks by the native Americans hundreds of years ago.