Someone earlier got me thinking. They said something like Cemex=Concrete=Keystone? so I searched "cemex keystone and found this. Does the Saguaro relate? Sign posts in the desert? If you have ever seen one, they are Giant and can been seen for miles. (the word keystone is in the 5th paragraph) just a random thought.

http://www.cemexnature.com/project/cemex-aggregates-cerrito-blanco-quarry-biodiversity-action-plan/