NARROWLEAF POPCORN FLOWER (?)
35 species of Cryptantha exist in Arizona, and these are very difficult to distinguish. According to the Bowers and Tekiela, Desert Tortoises feast on this plant.
These flowers were photographed in Sierra Blanca Canyon Wash in April 2005. Below: closeups of the flowers (left) and leaves (right): (Click on each image to enlarge it.)