This is a very common cactus at Big Bend. I only saw a few in blossom on this trip in April 2001. The brown flowered cactus blooms in a ring of maroonish brown blossoms around the center of the stem. It's spines are really dense as you can see in this photo, almost completely hiding the stem.

Photo Details: Nikon N90s, Nikon 85/2.8 Tilt Shift, Velvia, f11@250, Manfrotto CF4221 w/ Kirk BH-1.