Corey,
I live in Terlingua so I thought I would add some perspective.
First, I would say that in most years the 10" rainfall figure is closer to the norm over the whole area. Elevation does make a difference, but location also has a lot to do with it.
Second, Terlingua as zone 9 is right by the charts. Most years we get good freezes and usually have some freezing rain/sleet. Higher elevations also get colder and may get some snow. Five years ago we had a freak winter storm that took us down to 4 degrees F. for three straight days. That killed everything that wasn't very hardy. Last year our dog
water bowl did not even freeze.
Third, Your species list has many things I don't recognize off hand, but remember that Bill Mollison's lists may have plants adapted to Arizona's Sonoran Desert. There are many Sonoran plants that can cross over into the Chihuahuan Desert, but Saguaro Cactus would freeze here every year unless well protected. I grow apricots, pomegranates, and figs, but fight to keep them alive during the worst summer heat. In higher elevations I know some people who grow apples. We garden, but in the fall and spring. Getting water into the soil is a big challenge out here. Much of Terlingua Ranch (
TR) sits on gravel over Bentonite clay or directly on top of Bentonite. Other parts are on top of limestone, and other areas are on igneous formations. Each area has unique challenges. Almost all of
TR was overgrazed at some point during the last century and recovery is very slow. Some areas will not recover IMO without help, but others are showing progress.
Fourth, Land prices appear cheap, but there are usually reasons:
a) Access is a big deal. (
TR) is spread out over a couple hundred thousand acres. It is on the east and west sides of Hwy 118 for approximately 28 miles and north and south of Hwy 170 for 5+ miles. Tracts that front these highways carry a premium because they have all weather access and no access easement issues. The ranch road from Hwy 118 to
TR Lodge is paved except for the last ~ 3 miles and is maintained by Brewster County. Some tracts can be accessed from North County and South County Roads. These are dirt/gravel roads maintained by Brewster County. Other than these roads there are very few other county maintained roads that I am aware of. The rest of the
TR tracts are accessed via dirt/gravel roads that are maintained by
TR. I believe their website says there is something like 1,200 miles of dirt roads to access all the tracts on the ranch. Dirt/gravel roads are OK until it rains hard and then you realize how many creeks/streams you must cross to get to/from your place. The more remote a tract, the less frequently the road is maintained!
b) Electricity is available to a relatively small percentage of
TR tracts. If power is on a tract it will carry a premium. This is one of the reasons so many people out here live off-grid. It is cheaper to put in your
solar system than to get power extended to your tract.
c) Water is never a given. In Terlingua/Study Butte/Ghost Town area the Study Butte Water Supply Corp. provides potable water along Hwy 118 and Hwy 170. There may be a thousand
TR tracts that can access this water supply at this time. Everywhere else relies on rainwater catchment, hauled water and/or well water. You will find that practically everyone out here uses their roof to catch rainwater so it can be stored for later us. If it has a roof, it likely has gutters and tanks. There are some areas of
TR that have subsurface water that is good water at reasonable depths. Other areas the water may have very high mineral/salt loads, be very deep e.g. 800+ feet deep, or very slow delivery rates e.g. < 1 gpm. Other areas have NOT shown water potential at any reasonable depth.
Let me know if you have other questions.