This cactus is uncommon in California. It is a single stemmed-plant, and three separate individuals are seen here in proximity. East of Death Valley, March 17th 2012, Image I12-0895.
Silken Pincushion (Mammillaria bombycina) in cultivation at Ballarat, Victoria, Australia. Photographed on 18 September 2011.A native of eastern Jalisco, Mexico.www.inaturalist.org/observations/55467473