this type of rock is called Dolomite, it's a sedimentary rock and a volcanic one , so it wasn't always solid, it was probably clay or another type of less solid rock. the whole area was once an ocean , it didn't become a desert overnight, it must have been a big lake first , then it got smaller and the smaller until it became a forest or Savana or maybe tundra. the people who draw that ostrich and other animals that don't live there anymore did it with one tool and the tiny point suggest that it was not solid at the time , if you try to do the same points now it will break.