The barrenness of the American desert is broken up by a collection of rivers. The altitude of the Rocky Mountain collects enough moisture to fill the rivers that pour into the Southwest. Communities then gather around these rivers to collect the water and moisture, creating their own canals to divert this water into their crops, in a process called irrigation. Irrigation can also help keep the ground soft after the cold desert nights. This is absolutely vital to surviving in the west, since rain falls so little, and the soil is otherwise hostile without human intervention. In the Industrial Age, there were concerns about the American Southwest having enough water for their needs, but the smaller population and lack of plumbing or intensive gardening have lessened the burden. However, nations and tribes do fight over water rights, since if a state is to expand, it would have be along the river lines. It has also given the governors absolute power over their subjects.
Communities are small, but very tightly wound together. All villages and cities tend to center around the major rivers used for irrigation and wells. This helps foster consolidated population densities. The denizens in Hydraulic nations tend to share common languages and have access to similar goods. We also see small but impressive middle-to upper classes that can concentrate on craftsmanship, education and health. This is because access to civilization is much closer, and there is no warrior class, but rather the Emperor's own private army. As such, the desert kingdoms are often much more advanced in fields like astronomy and medicine.
The exception is out deeper in the desert, where we see wandering bands of nomadic herdsmen. These people may be subjects to the Governor, and have to pay him tribute or have their sons and daughters conscripted into military, servant or even bridal duties. They are nominally considered parts of these kingdoms, but they often do not get along well with their farmer counterparts, and may be persecuted or treated like second class citizens.
The desert farmers have somewhat similar diets to those in the south, though there's less a focus on vegtables (Which tend to thrive in wetter regions) and rice (Which is downright wasteful in the desert). They often focus on crops that don't need as much water like blue corn, chile peppers, mllet and various beans. Fruits are very common, especialy oranges and dates. Most cheese tends to come from goats, who are the most valuable livestock out in the deserts, since they are highly durable and their stomachs can digest almost anything.
Clothes:Along the river banks, farmers and other denizens may dress much like they do in the American south--with loincloths and and ponchos and wide-brimmed hats. If straw is hard to come by, or the rich wish not to look like peasants, they may wear pieces of cloth similar to the keffaut, made out of cotton. It's also common to put black makeup around's one's eyes to block the rays of the sun. However, for villagers outside the rivers, where there is less moisture and buildings to mitigate the sun's rays, protection becomes immensely important. Here, loose, baggy clothes are used, and bandanas to protect them from sandstorms. Once we start getting out into the nomad territories, they may dress much like other herdsmen, however their clothes are looser and more colorful. Many people in the desert may also keep cloaks handy, for the nightfall turns the climate from blistering heat to bitter cold.
Much of the kingdoms are traversed along the life-giving rivers the communties cling to. Barges are built for the governor and his court to do business or just sight-see. They are also very important for transporting the infantry from one corner of the nation to another. Because most of the Hydraulic Empires in North America are located near mountains, wood isn't as hard to get. But it can still be expensive and something of a luxury. Therefore, most of the farmers and traders traverse by land. They ride durable beasts like burros and camels. The wealthy upper classes may still use horses for battle or envoys, since they will have large enough caravans to support less hardy beasts.
The isolation of these nations from the rest of the world, in addition to each other, has allowed belief systems to wildly diverge from the Christian east. A large element of many beliefs around here is the obsessing with the stars. The skies are very clear at night, and astronomy (as well as astrology) are valued skills out west. Many myths and folklore involve chariots of the gods, great ships that traverse the stars, and even creaturess from beyond who crashed out in the far reaches of the desert. Because of the lack of moisture, scholars are able to keep advancements and records very well documented.