Sclerocactus parviflorus
Cactaceae (Cactus Family)

Semi-desert, foothills.  Woodlands, openings  Spring.
Hunter Canyon Trail, Utah, May 3, 2005.

As this picture indicates, S. parviflorus does produce clustered plants.  It is, however, far more common to find unbranched, solitary stems.   The pictured plants are about seven inches tall.