Steam - also contains some info on the nature of quasi-elemental planes in general
And yet in open defiance of their reason, it exists. In its every salt flat, salt dome, salt lake, and salt marsh, it exists. See it in your mind's eye out to the margarita-rim horizon, feel it strip the phlegm from your throat with every cottonmouthed breath - and do not think to limit it to mere piles of table salt:
Layering impossibility on impossibility, the plane should be a dead world, a still and silent world, but it lives. Its life is stolen, its deadness truly undeath. Look to the vault of its heavens: the eternal dusk of this morbid realm turns blue. The vampire begins to drink, with an osmotic pressure that can rupture the very membrane of the cosmos. The sky bursts, and the world floods, though it does not drown in the flooding. Its thirst is too great for that. Caught-up fish fall and gasp their last then desiccate, leaving a bounty for scavengers that could last buried for centuries. As quickly as the water comes it disappears down countless crystal-crack capillaries. Beneath the surface the water moves unpredictably - sometimes seeping up in brackish pools, or spilling out the sides of valleys into sudden rivers. Some even drips down into the churning molten reactors where radiotrophic micro-biomes bloom, and erupts back to the surface in irradiated geysers, a rare few carrying the force to shatter mountains. The greatest share of the water's volume will never be seen on the surface again.
This is how the plane lives. This is how it supports the growth of its native life. Here there are lizards who live the near-full length of their lives ensconced in leathery eggs, rolling about the plane like tumbleweeds. When a skyburst comes they hatch, eat like locusts, breed and lay the next generation, then die. There are black yeasts, tardigrades the size of wild hogs, glassworts, lichens, algaes, camels, cladocerans, flamingos, elephants, snakes, plovers, archaean halophile slime-molds, brine shrimp, brackrice, cacti, vultures, crocodiles, hop-crabs, mangroves that migrate by the marching of their hyrdrostatic roots, and people, people too, all living by the oases of reliable water-seeps or adapted to live between the rare occasions when deluges rain.
A healthy human on the prime material plane will be composed of a roughly-even mix of fire, water, earth, and air. Should they move to one of the elemental planes and remain there some time, breathing in and consuming its substance, this balance will change. On the more positively-aspected planes this process will be additive, invigorating, followed by a gradual crowding-out of any opposed composition. On the more negatively-aspected planes it's a decidedly more unpleasant-feeling process - a drainage, with material then flowing in to fill the void left by the plane. Come back before the process has run its course, and your body can still re-acclimate - though you'll be very sick for about a week. It should be noted that this process can occur with animals, plants, just about anything with something resembling most of the parts of a metabolism.
Once the quasi-elemental plane of salt (just "The Salt" to those accustomed to it) genasifies you, it'll have got its fangs into you. You'll become gaunt - even if fat you'll have lost the comfortable bloat of water - and crumbly grains will fall from your eyes instead of tears. On the bright side, you'll be able to survive much longer without water and much higher levels of salinity, even becoming able to enter a state of cryptobiosis if need be.
Some unfortunate souls go down a different path. They suffer a thirst so grievous they'd cut their own mother's throat to take a sip from the blood that'd spurt from it, and transform into beings called "crust vampires". They burrow deep into the plane and extend their veins over whole regions, slurping up any blood that spills on the ground throughout. These crust vampires are hunted as much as they hunt, becoming gargantuan stores of fluid much like the repletes of honeypot ants.
Most of the human population of the Salt is made up of genasi, and most of these genasi live in villages or nomadic clans in the salt marshes that spring up around water-seeps. They make their means by hunting, digging up the preserved meat and kelp which falls from the sky, farming in rice-fish (or some other halotolerant crop-and-creature combo) systems, and carving out and caulking up cisterns and artificial ponds to painstakingly extend productive areas over generations. Tools are mostly bone and shell - fuel is scarce, being mostly dried dung and reeds, so metal is reserved for weapons and magical implements. Travel and trade between these marshes in typically done in caravans of sleds pulled by teams of pick-beaked ostriches. The strongest and wisest are able, from atop the Salt's highest peaks, to swim up the deluge of a skyburst, entering back into the plane of water. Astronomers who can predict skybursts are also honoured among them.
The most populous polity of salt-genasi known to those outside the plane is called Dredge - a league of city-states along the shore of one of the plane's few seas. This sea, in a cold and deep-set section of the plane, is able to exist due to a virtuous cycle between its melting ice and dissolving salt sustaining it. Its temperature is well below water's normal freezing point, and so nothing is able to survive within it - meaning nothing but the genasi can consume the bounty of skyburst-dropped corpses in its depths. The sheer mind-boggling calories that Dredge's fleets are able to bring up from the sea feed its population and military supremacy - though with exponential growth involved, who can say how long any of it lasts.
The Salt is a harsh place for its children, and much harsher still for those that it hasn't adopted. They still come however, chasing its riches or its secrets, most to die or be drained dry.
The Silver Serpent School: A prestigious and powerful school of alchemy on the prime material, who are able to open a portal to the plane of salt through the artifact called the Gate of Horned Lead.
They administrate vast and terrible mines for the plane's metallic salts, which they are able to transmute into marvelous powders and bombs, and more mundane products besides, worked by slaves bought from Dredge and their debtors back home - trading in return cutting-edge weaponry and automata, both fueled by the same volatile alchemicana.
The Silver Serpent School is possessed at its upper end - the learnéd masters - by the metaphor of the crucible. Only by passing through the crucible of utter annihilation - the negative energy plane - do they believe they can achieve perfection, passing from life to undeath to something further beyond. The actual workhorses of the School (not counting its slaves) - the young and hungry apprentices - have not been properly instilled with this obsession. They are universally interested in the school as a business, and a circle of forward-thinking members are experimenting to invent a method to synthesize food from the plane's salts that could replace the bounty of Dredge's sea once it's exhausted, to deepen their dependency on the school.
The Grand Gourmands: In the days before that crown of the cosmos was broken, a hundred cults sprang up in Sigil around a goddess with a hundred names: the Empress in Red, She Who Reigns from a Throne of Razors, Mother of Ecstasies, Lady of Pain, Malcanthet, Tabrach-Ti, Mistress of Bronze, Queen of the Succubi, and so on and so on. Blamed for the city's decadence and the collapse of its power, these cults scattered across the planes after Sigil's breaking.
The Grand Gourmands (who worship their goddess by the name "Our Savoured One") settled in the plane of salt, drawn by its culinary offerings. Their cultic magic lets them live off luxury alone - nutrition is nothing to them if they have their sweets and treats, and a blizzard can be shrugged off if they're in silken and bejeweled attire. They are widely hated by locals as their feasts can strip-mine delicate ecosystems for leagues, yet the Gourmands boast powerful patrons from every corner who they host and entertain, and who can be called on for assistance if they're attacked.
Ultimately, the Grand Gourmands seek to terraform the Salt, slake its thirst for their good. To this end they seek the soul of the Tower of Babel, rumoured to be hidden away on the plane by Enoch, to turn it into a tool that could pierce the heavens and bring about a skyburst whenever they so desire.
The Nameless Cities: There are mountains carved into cities on the Salt, or cities as large as mountains, and within these cities are mummified legions - any city seems to have more mummies (none bearing typical genasi-features) within it than there are people for hundreds of miles around. Nobody's stayed in one long enough to do a proper count. Those who try don't come back.
There appears to be a united material culture and writing system between these nameless cities - though there is no obvious antecedent or descendant of either on the Salt or the prime material. Their mummies tend to be posed either in military formation - rank upon rank in rusted arms and armour - or in moments of peaked personal triumph - a ruler's coronation, an athlete's victory in a chariot race, lovers' consummation of their marriage, and so on. Disturbance of the latter sort of tableau tends to result in immediate bloody retribution - but it must be said that this can only be assumed from the gory scenes that apparently result from such an act. Such disturbances are not the only danger of the nameless cities, for whole exploratory teams have disappeared nowhere near these tableaux.
Fools still enter the nameless cities in search of their preserved treasures, and to retrieve childerlicks - it's possible for women to become pregnant by licking a nameless city mummy, so many are willing to pay well for parts of a mummy taken from a suitably-heroic tableau - these parts are called childerlicks.
The living substance of the Salt itself, salt elementals are an enigmatic bunch, thankfully expressing the place's thirst only in obtuse ways.
Salt-genasi tell tales of the saltating mephits and their leaping dances out in the wastes - all who come across them are drawn in to join them. In response one must throw a handful of pickles, or else you'll be compelled to dance until you sweat out your last drop of moisture and crumble to dust.
There are baths too in the wastes, not the commonplace mirages but genuine fluid, though they contain the dissolved forms of Epsom salt elementals. They tempt you to float a while within them, so that they might imbue you with visions of events near and far, visions of prophesied futures, which if followed will lead you to fulfilling the greater will of the plane.
The mightiest of the salt elementals exist within those aforementioned molten reactors - yellowcake titans swimming in oceanic thermal batteries. They are thankfully alien, as if anyone or anything could sway such a being to their side they could surely shake the spokes of the Great Wheel.