There are over 300 varieties of hummingbirds in the world with less than 20 kinds in North America. http://birding.about.com/od/birdprofiles/ig/Hummingbirds-of-North-America/
In California we have thirteen kinds of hummingbirds. Anna's, Black-chinned, Costa's, Rufous, Calliope, Allen's, Broad-tailed, Broad-billed, Blue-throated, Violet-crowned, Ruby-throated, Xantus', Green Violet-ear. In our back yard, we have identified the Black chinned, Anna’s, and Allen’s Hummingbirds.
I don’t know the maximum elevation at which you will find hummingbirds but I have seen them at the feeder attached to the lookout on top of Buck Rock in Sequoia National Park (8,500’) and even higher while backpacking the trails of the Sierras. They tend to hover less and perch more at higher altitude.
My wife has planted flowering shrubs in the yard to attract Hummingbirds, who drink the nectar. The most popular color flower is red. Our shrubs include Pineapple sage, Butterfly Bush, California Fuchsia, Columbine and Penstemon.
Hummingbirds also eat insects, larva and spiders, which provide nutrients not available in nectar and sugar water. They must eat continually because of their high metabolism. The metabolism supports wing beats that can exceed 100 per second and heartbeats that can exceed 1,000 per minute. "Eating like a bird" means eating their weight in food daily for hummingbirds.
While I like to watch eagles, hawks or even vultures soar effortlessly on the updrafts along bluffs, the flight of the hummingbirds amaze me as they fly in so many directions in such a short period of time. They are like little helicopters. I hear them overhead by the sound of their wings but not the high-pitched vocalizations.
We have three one pint feeders hanging from our fascia board in the back and one in the front which attract about 30-40 hummingbirds. Thus our feeders need to be refilled with sugar water daily in the summer. When we forget, they remind us by hovering up by the window or chirping at my wife (my wife can hear them).
On a couple of occasions, they have flown into the window and two have been killed. It is sad to see these beautiful birds lying lifeless on our patio. Once, I picked up one and stroked it gently in my hand. It awakened and flew away.