It's a mass of hard rock that has resisted erosion even though the plateau around it has been destroyed. The Uluru is an example. :)
because if there are no deserts there are no diff. plants like cactus. because other animals can't live in cold or fine weather others can only live in hot places. because if there are cold weather...
they were formed by sand and the wind blew it around.
rain shadow effect
they are formed by volcanic processes that give rise to a rock resistant to erosion