Museum records indicate that peak diversity for bees is in the warm North American deserts and around the Mediterranean Sea, however no methodical studies had been done in these areas. An intensive survey of Chihuahuan Desert bees in the San Bernardino Valley of Mexico and the United States confirmed that the concentration of bee species is among the greatest in the world (Minckley 2008). Interestingly, a comparison with the extensive collections in the American Museum of Natural History indicate many more bee species in this region (Minckley & Ascher 2013). A partial list of the San Bernardino Valley bee fauna is available here.
Bee surveys are most recently being done on Cienega Ranch, Arizona in Chihuahuan Desert Grassland. The extensive ecological restoration being done on the ranch opens many questions about bees.
The University of Arizona is where the entire botanical and entomological collections from the projects are deposited.