Haha, yeah I'd like to know that as well... the only thing that seems to grow here (or at least, seems to get planted here) is Siberian Elm and Cottonwood. Definitely would advise the Cottonwood over the disgrace known as Siberian Elm. Otherwise, I really haven't seen anything, but maybe people here are just unimaginative.

Bur oak might do okay. From what I understand, trees can't really naturally establish with less than 15 inches of rain a year - That's why so much of the plains is grassland.

could look for some of the natives of turkey or similar spots.

couldnt help but notice the denver botanical garden.has tons of crabapples interestingly enough.

Thinking about this a bit more... with irrigation, I've seen a few decent sized honey locust, Silver Maple and ash (not sure which species) around here. However, *only* with irrigation. Without it, they're all gonners.

Also, with irrigation... a species of locust (Robinia) native out west, (Idaho locust?) seems to do alright.

Finally, yes there are a lot of Crabapples. But I was thinking more along the lines of shade trees. And yes, they still need plenty of irrigation.

The conditions you specify are going to have VERY few trees able to survive those conditions, and certainly very few large trees. Most forest in the west are composed of 2-3 tree species, while eastern forest may have 30. You best bet are probable going to be western species conifers IMHO. Pinion and Ponderosa Pine comes immediately to mind.

Arktrees

Ponderosa still generally needs more than 15" of rain per year, at least to get any size out of it. Pinyon doesn't, but of course it grows ridiculously slowly so doesn't really count as a "tree".

Cooperative Extension will have recommendations.

Taxodium distichum
Ginkgo biloba
Celtis occidentalis
Cornus officinalis
Cotinus coggygria
Hibiscus syriacus
Zelkova serrata

Dax

Cotinus obovatus NEEDS it to be rather dry.

I think something that's overlooked with this is an element of this kind of climate which hurts a lot of trees, that being the very short growing season. Where I am, even though its zone 5B, the growing season is only 90 days long on average.

Catclaw Acacia, Honey Mesquite, and Screwbean Mesquite are trees that are listed to survive with as little as 6" of water. The first two are rated at -13 F and the last at -3 F. Not sure if that will make Z5 requirements.

Probably won't cut it, but guess it could be attempted.

Highly doubtful.

you've answered your own question.

on another note, of interest may be the difference between c3 and c4 plants.

Chestnut oak Quercus Prinus will grow on rocky dry slopes. Zone 4 hardy. Should grow decent on dry sites, it;s rapid growing on good sites.

Dry by eastern standards is wet by western standards. Chestnut oak would not cut it.

You're pretty much limited to sagebrush and buffalo grass there. I don't think there's much else that could take the extreme conditions. You could try bristlecone pine, but that's a slow grower, too. There really are no fast-growing trees that will grow in a desert climate. The only ones that would require warm winter temperatures.

I don't think I'll complain about our wet weather too much! It is "really dry" here right now (We haven't had rain in over a week - May is our second highest rainfall month, July the wettest.), so I've had to water some things. I hope it's not like this all summer!

The only trees that I've seen survive on their own in the wetter, low elevation areas of the state with 15" of precip are chinese (siberian) elm and russian olive, however these usually take some help to put in a snow fence upwind to leave drifts where the trees are planted and provide additional moisture. They will probably get enough moisture to grow 10-12' high, then lose branches in dry years and generally look about 1/2 dead.

However, if you go to an area with ground water, such as near a stream or spring, then you have lots of choices--cottonwoods, other poplars, ash, linden, boxelder, apples, honey locust, black walnut, and others. The key is whether you want to irrigate or have groundwater for the trees to survive on and your elevation. Otherwise, you go with what appear to be half dead bushes or just stick with bushes such as caragana or lilac and some evergreens such as junipers.