I just spent the months of March and April out in the field doing archaeological monitoring for a construction project (not really as exciting as it might sound). There was very little actual archaeology where most of the construction took place, but there was cactus! The most common cactus in much of the project area is the endangered Sclerocactus mesae-verdae (aka the Mesa Verde Cactus). Because this cactus is endangered there was also a biological monitor present to make sure construction did not disturb them. This meant that all know locations of the cacti were clearly marked which made it easy for me to locate and photograph them. Below are links to some facts sheets on the species and some of my better photos, enjoy!
http://www.southwestlearning.org/download_product/1716/0
http://www.nndfw.org/nnhp/Plants/scmeve.pdf
http://www.fws.gov/southwest/es/documents/r2es/mesa_verde_cactus_5-year_review_jan2011.pdf