Many of these bees were seen flying around a rocky outcrop on the mountain, chasing each other and defending territories. My friends saw some of them chase another individual "the size of a golf ball", which I'm guessing would be a female. The closest thing I can find on here is Xylocopa californica arizonensis, but the photos on here of that species lack the pale-colored pile and the intense blue coloration (which looks even more vivid in person, it's hard to get the camera to capture it).