According to Epple (cited on main Wildflower page, p.55), there are fifteen species of Rumex, a perennial herb, in Arizona, and we are not very familiar with them. The accompanying photos may show two different species. One kind is known as "Desert Rhubarb", and one is used as a potherb. The tubers are sometimes used for tanning.
Both of these photographs were taken in March 2005 in Hot Springs Canyon. Click on the image below right for a closeup of the inflorescence.