Plants that use water efficiently, what a provocative and broad subject to touch on, Joe. You're going to make me stretch for this one.
first, simplest and easiest answer is that for true drought tolerance
you really want to find a nearby Native Plant Society and see what they
can suggest. Any plants native to your area will have been
fantastically adapted by years and decades and centuries of evolution
to be adapted to whatever climactic problems your area might have. I am
sure the sagebrush species in your area has seen droughts that we can
only imagine in our worst nightmares. Most of these plants aren't going
to be edible for humans though, so if your aim is going to be an edible
garden you will need to do some irrigating, but there's a lot of ways
to do this so that you are using water way more effeciently than your
average farm. Agriculture tends to waste a lot of water, but there's
really very little reason to.
The first thing to work on is delivery method and timing of water. On our farm we use a drip irrigation for the vast majority of the land and only water early in the morning. Drip irrigation is great not only because it delivers water directly to the soil, with little chance of evaporating before soaking in, but also by applying water slowly there is little chance of run off. A major bonus for whoever is tending the garden is that it also only applies water to the small area where the plants you like are growing, rather than also feeding lots of weeds all over the place.
early in the morning (ideally pre-dawn) is not only great for water
saving, but it is also when the vast majority of natural rain falls
during the summers in most climates, so most plants are going to be
well adapted to it. If you think about it, if you water just before
dawn the water is just soaking into the area where the roots are about
the time when the photosynthesis factories in the leaves are getting
powered up and so the timing is just naturally going to be most
advantageous to plant growth.
Other ways to save water include planting in an area that doesn't get full sun all day, of course then you have to choose plants that won't freak out with that kind of treatment. Also just “shading” the soil by laying a mulch down can reduce evaporation a lot, as well as add extra habitat for tons of fantastic soil invertebrates. And they're my favorite. Planting things slightly closer together then suggested by the seed packages will also help to shade the soil.
back to the original question, what sort of plants to choose. An
embarassingly good rule of thumb for finding drought tolerant plants is
to look through seed catalogs that carry heirloom seeds and pick out
anyones that have Native American names. Part of why there is some sort
of weird fiction that all the people on this continent were doing
before Europeans made it here was hunting and gathering is that their
agriculture had little-to-no irrigation attached to it. They also
eschewed things like monocultures and intensive weeding, but that's a
whole other topic to cover at a later date. So yeah, there area a lot
of fabulous beans that are drought tolerant (look at Seed Savers as an
excellent company for these). I'm growing Arikara Yellow, Hidatsa Red
and Painted Pony just to give you an idea. Lots of types of corn are
also amazingly drought tolerant, though not the super sweet kinds that
we tend to eat in this country, more the kinds that you would make
cornmeal or other delicious stuff out of. Dry corn is an amazing crop
for storage of course.
Besides just plants that are drought tolerant are ones that just need water for part of their growing cycle. Potatoes (and it is probably a little too late to plant them now) only need water up until the leaves start to yellow a little and then you actually should turn it off so they don't rot. Sweet Potatoes similarly get their water cut off part way through production.
All right, this is starting to spill on to a second page of the word document so I've likely bored you all to tears by now. But if you'd like me to ramble on for pages about another topic, suggest one in the comments!