White has actually given two of the three desert kingdoms their own pages, leaving only New Mexico mystery. The territory has extended into Arizona, and even some of Texas. The desert shepherds and goatherds may play a very large role in New Mexico. The husbandry map combined with the West Map shows that within New Mexico's borders, we see quite a few nomadic tribes. They may even make up half the population. This is kind of fitting as New Mexico and Arizona have always been more "Wild West" than the other desert states, and still boast a few ranches. Most are probably shepherds and goatherds, but it might be possible there are cattlers here and there. Another interesting thing is that the major cities seem to mostly be in the eastern half of the nation. However, there are settlements on the Gila river. I wonder if they're more spread out, and most resemble the old Native American cultures which have likely blurred over history. The religion map says "New Age", and I'm not sure what that is, or why primarily Catholic New Mexico would be practicing that. It's possible that, with the sun belt's collapse, people were looking for drastic new answers. The religions of the modern westerns world come mostly from the desert (The same desert, in fact), so it probably makes sense that if anything dramatically different were to pop up, here would be the place. And it would probably take just one eccentric autocrat to impose his new faith one everybody.
Speaking of which, while White has talked about Deseret and California specifically, he hasn't really gotten into their respective faiths. I'll get into them on the religions page, but both are real world religions, and considered by some to be especially peculiar. The Church of Latter Days Saints established a foothold in the settler days, and today Utah and its surrounding areas are very strongly and uniquely Mormon country. In addition to its demographics, isolation, and that harder times are Churchy times, that Mormons tend to have survivalist leanings makes its endurance into Medieval America all the more logical. Probably the biggest contributors to Hurricane Katrina relief were Mormon organizations. The Church of Scientology's prominence is a little more of a headscratcher. There are not any adherents, (and in the days since White first created it site, it has suffered P.R. disaster after disaster.) This maybe trying to take the stereotype of the Los Angeles airhead to its logical conclusion, and that it's the religion most associated with movie stars may mean a sort of sci-fi, movie inspired religious doctrine. I would bet Emperors often claim they're made into stars upon death--and local astronomers are bribed to name stars after their recently departed rulers.
The "desert" graphic has horse archery as the prime mode of combat but from all appearances Desert and California have their share of heavy cavalry. Because there's no "knightly" class in the Hydraulic Empires, and it appears the armies must be celibate, and because their general is also their spiritual leader, I've presumed that the warriors here operate much like the Knights Templar (Who also got their start in the arid Crusader States), and considering the Church of Latter Days Saints calls their HQ a Temple, my own creative contribution to the Medieval American World is that "Templar" is a unique sort of class of celibate, desert-based lancers