Depending on local conditions, the various species of American Southwest cacti typically bloom in late spring, May to early June. Death Valley's terrain is famously harsh due to its extremes of heat, dryness, and soil salinity, but cactus species that can be seen here include cottontop barrel, silver cholla, and beavertail cactus. Desert wildflowers are currently starting to bloom in some of the park's lower elevations, and you should start to see some spring flowers on the cacti toward the end of April. Check with the park for specifics and best viewing locales. More info at: http://www.nps.gov/deva/naturescience/wildflower-update-2010.htm