The centipede in your photo is the common desert centipede, scientific name: Scolopendra polymorpha, in the family Scolopendridae. It is one of two large centipede species found in Arizona and other parts of the southwest US. These centipedes are normally active at night, when they crawl around seeking insects and small animals as prey. During the day they are usually hidden under rocks, logs and other protected places so are seldom seen. The first pair of legs have been modified into venom injecting structures to capture their prey. They are not considered to be dangerous to humans, but they can inflict a very painful bite. I have include some links below to webpages with more information about these centipedes.

https://en.wikipedia.org/wiki/Scolopendra_polymorpha

https://www.desertmuseum.org/kids/oz/long-fact-sheets/Desert%20Centipede.php

http://www.wci.colostate.edu/Assets/pdf/CIIFactSheets/CommonDesertCentipede.pdf