Source: Wikipedia
Lampropeltis pyromelana, the Arizona mountain kingsnake, is a species of snake native to Arizona. It can grow up to 36 inches (910 mm) in length.

Within Arizona, L. pyromelana has a discontinuous range extending from the extreme northwestern corner of the state, across the central mountain ranges and the Mogollon Rim, into the "sky island" mountain ranges of the southeast. They can be found at elevations ranging from 3,000–9,000 feet (910–2,740 m) in a variety of habitats from chaparral to conifer forests, often near streams or springs and associated with juniper woodland.

L. pyromelana feeds on lizards, rodents and nestling birds. It tends to spend the daytime among rocks, logs, or dense clumps of vegetation.

Source: http://www.reptilesofaz.org/
Non-Venomous, up to 43", may climb trees/boulders, hibernates in cold months. When captured this snake does not hesitate to bite and discharge foul-smelling musk and feces.

Note: if the head is all black it may be Lampropeltis triangulum celaenops