Setaria grisebachii
A bristlegrass with sparse bristles & a looser inflorescence than the other Setarias. The plants I've seen were also quite small (less than 9 inches), but it does get larger.
An inflorescence along the Pine Tree Trail at Aguirre Springs on the east side of the Organ Mts., 9/24/05.
Plant habit at Aguirre Springs, 9/24/05.