If you are the one who created the crag you're also able to delete it. You can find the delete option by going to the topo view of the crag and then clicking the edit button on the right.
If you don't see a delete-option in the drop down menu it means that some information has been added to the crag which prevents deleting it. This includes routes/pictures etc.
If you need to delete a crag which has information, you first need to delete all the pictures and routes from it. Once it's "empty" the delete-option will appear.