I don't know where this is, but I do know Colorado. There are lots of streams here, but they dry up in the summer. As far as I know, there are only four real "rivers: - the Platte, the Arkansas, the Colorado, and the Rio Grande, all fed by the streams. And as said above, every drop of water in the state have been claimed, some of the rights going back to the 1870s, and many rights are out of state, AND the DoWR keeps a close watch on what's being used, via aircraft and satellite. Get caught pumping irrigation water out of a river or lake? They'd likely hang you from the nearest tree.
I'm figuring #1... Because farming is hard.
Yes, and it takes a lot of knowledge. It's a fools errand, especially at 10,000 feet. I've hunted elk over 10K, but I live at 4,700. Anybody from sea level will be violently ill until they get acclimated. Add to the fact that by March, there will be 10 to 15 FEET of snow above 10K feet, and sometimes it's August before it's all gone, to return in September.