This image of andesite shows a piece of the resistant rock that protects the top of Tempe Butte.  Andesite is an extrusive igneous rock (light blue in the diagram below).  It is closer to basalt than rhyolite in its chemistry and mineralogy (more mafic in the diagram below).  Most of the andesite has minerals too small for you to see with the naked eye. The only crystals you can see are those that started to crystallize before the lava erupted. These white crystals, called pheneocrysts, are embedded in a dark fine grained matrix.  This rock type started as a lava flow from a nearby, now inactive volcano.  The exact location of this volcano is uncertain. 

This diagram shows the relationship of andesite to other common igneous rocks.  You will see an example of rhyolite near the end of this trip. 

If you are interested, there are some links below to help you better understand how andesite relates to other rock types. 

Helpful Links:

Rock Primer
Igneous Rock Site Introduction to the Beginner ,
Rock Landforms of Austalia and New Zealand with Focus on Different types of Rock Types