Family: Buckwheat (Polygonaceae)
Size: Approx. 0.25 in.
Notes: I'm not absolutely certain of this ID. There are probably another 40 specied of Eriogonum in AZ to check out yet. Flower clusters with no stems on almost bare stalks. Scattered leaves go up the stems from a leafier base. The plant is 18 in. - 2 ft. high, and about the same across. 53 species of Eriogonum in Arizona.
This plant is found on the Appleton-Whittell Research Ranch Working Check list of flora.
Sorrel Buckwheat plant profile on the USDA Plants server.