According to the Sibley guide, there are sixteen species of hummingbirds to be found in the American West, but in our county only six species have ever been noted. Of them only the Anna's Hummingbird is a year-round resident. Black-chinned Hummingbirds are relatively common during the summer, and Rufous Hummingbirds migrate through the region in the fall and spring. The other three are rarely seen.
Overall the lack of diversity simplifies hummingbird identification at our feeder. The orange-colored Rufous can't be mistaken, and the Black-chinned will have purple iridescence around the neck. The Anna's are magenta, although it's off a bit in these pictures because of the reflection of the feeder.
I do wish they would get along at our feeder. They are territorial about their food supply and will spend more time chasing intruders than they do eating!