Crematogaster arizonensis
I've mostly seen these ants on paloverde trees. They were nesting in the dead wood, and forage in streams up and down the tree.


Click on the images below to see a larger version

Crematogaster arizonensis worker on paloverde tree bark
Crematogaster arizonensis worker on paloverde tree bark
Crematogaster arizonensis worker on paloverde tree bark.
Crematogaster arizonensis worker on paloverde tree bark.
Top view of Crematogaster arizonensis worker on paloverde tree bark.
Top view of Crematogaster arizonensis worker on paloverde tree bark.
Side view of Crematogaster arizonensis worker on paloverde tree bark.
Side view of Crematogaster arizonensis worker on paloverde tree bark.
Crematogaster arizonensis worker on my fingers for scale.
Crematogaster arizonensis worker on my fingers for scale.
Crematogaster arizonensis workers on paloverde tree bark.
Crematogaster arizonensis workers on paloverde tree bark.
Crematogaster arizonensis workers on paloverde tree bark.
Crematogaster arizonensis workers on paloverde tree bark.