[@Scarescrow] Welcome! I'll try to answer as best I can, subject to us figuring out more details for the lore.

The Second Sun was a single-use weapon, now discarded. It fired probably one or two decades ago, though we're a little fuzzy on the exact time- long enough for conditions to stabilise beyond 'everything's still 100% on fire', short enough for survivors to stick around and invasives not to take over completely.

I'm not inclined to play around too much with global solar radiation, since there's not much the players can actually do about that other than constantly worry about protective gear and sunblock. So the magnetic field and ozone layer are likely still intact-ish. Cancer rates high, though. Plenty of ruined nuclear engines around too.

Volcanoes, unlikely, impact-based tsunamis and earthquakes, definitely, both from falling spacecraft and falling debris from the shattered moon. Global super-hurricanes, sure, warming does that. Continent-sized forest fires outside the Plateau, definitely, at least while there were forests left to burn. Bioweapons and nanyte shenanigans, sure.

For some details about the locals we've thought up so far, here: Details on biomes!

[hider=North Sector: Coal Forest]
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The air of Cambria is heavy with blasted oceans. In the Morass, dense clouds from the north are trapped against the mountains, delivering fog and heavy rain, obscuring the desolation below. A cloud forest has formed here, and is threaded with a million streams, and bogs and shallow rivers come and go with the years.

The trees here are strange and old. Grand scaly ferns compete with puzzle-trees and puzzle-grass, and clubmosses rise, like towers without a single branch, to cast their shade between them. In the waters crawl nymphs and tadpoles of abnormal size, which grow into dragonflies and amphibians larger still. Some are stout enough to roam the damp earth, digging out great headless mites. They dare not look into the deeper burrows, where myriapods may be found even larger than they.

This far north, the lines between reptile, mammal and salamander are not yet clear. Synapsids wander and rumble their calls in the fog, some lumbering and scaly, warming themselves with solar sails, and others... less patient. Cynodonts groom each other's fur and snap at the winged lizards that glide above, chasing down the tusked and dog-like lystrosaurs if they have the courage to face such a heavy beast. If not, they lounge at water's edge, watching the armoured fish suck up specks of nothing in the mud, and bolting when amphibians swallow them in turn.

As the air warms, the cloud forest retreats slowly up and up the mountains, and so it has preserved its fantastic diversity perhaps better than any other part of the plateau. It will only last so long. There is only so much higher they can flee.
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[hider=South Sector: Conifer Woods]
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Where the land is higher, the ground is drier, and what rivers do flow down from the mountains feed into dryland lakes. Cycads fruit and form oases in the arid woods, and grand conifers stand alone among stones. Here a great many reptiles compete for the water and food, and as the billabongs grow smaller each year, the competition gets fiercer. Crocodiles built like boars arise to chase in the day, when sun is hot, and nothosaurs built like lizards lay claim to the lakes and the streams, sunning themselves on webbed feet before they fish.

Stocky archosaurs, horned shringas and broad-headed rhyncos, wander in search of food. They are hounded by slender coelophysid dinosaurs, but when the snap of a heavy beak is too frightening, or a small head is tucked under spiked and plated shoulders, the young theropods scatter to snap at stoneflies and lacewings, and roaches of every size and colour. The roaches, at least, do well.

Here, we see Cambria's last remaining sauropods, and they are small compared to their family- but who's counting? Standing two or three meters tall at the shoulder, they seem even larger on two legs, with their necks stretched high to graze the treetops. Long-tailed dactyls perch for a moment between a stegosaur's spikes before fluttering on to their nests, once among trees and now, ever more often, among pylons.
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[hider=East Sector: Prairie]
At last we have come upon the birds and the bees, though the birds have teeth and claws and long bony tails. The bees at least seem normal enough, and the foliage is recognisable: figs and flowers, grasses and sycamores. The familiarity only makes it easier to spot the sickness among the leaves. But for now, the grazing is still good. The wildlife eats well, and it shows.

Like wild cattle, hadrosaurs lay down in their hundreds to chew cud, and like jackals, dromaeosaurs follow in hope of a straggler. Their feathers are bright, their bodies warm, and where they can, they chase their larger ostrich-like sisters across the fields. The latter are called Hexing, and the former, of course, raptors.

All across the south, mammals scamper and sometimes prowl, badger-like. Troodons chase them in the dusk like avian foxes, getting up to all sorts of mischief around the CCF headquarters. All are wary not to be snapped up by the huge azhdarchs that peer down from above. They are not the most fearsome of the Plateau's predators, but they are the largest, and they see far from the sky and their towering necks. Those who die and are not defended swiftly disappear down their massive beaks, perhaps taken to the mountains to be fed to their young.

And all the while, a family of shark-toothed tyrants watches, raising their own hungry chicks where they can. The herds on which they feed are a fraction of what they were, and the giant theropods hang by a thread, a single wavering link at the top of a once-grand tower of life that now threatens to collapse.
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[hider=Dead Coast]
Unlike the altitudinal borders of the Morass or the maze of cliffs and mesas beyond the arid woods, the prairie has no fixed eastern edge. It fades slowly away, becomes humid and sickly, the verdant grasses taken over little by little by alien weeds clamouring for the only fertile ground left on the planet.

Dragons walk here. Huge hexapedal aliens tear up the turf and spawn by fission, consuming anything organic to fill their lobes with alkane fuel. Once a domestic transgenesyte, they now roam wild with no one to harvest them, swollen with volatile fluid and burning it off as they feed. Soon enough the grasses are replaced by self-replicating biofibre mesh, a wild colony of nanytes too foreign to be called flora, growing tangles of razor wire with which to defend itself.

Altitude falls further. Huge trees have taken over, perfect, solitary, pretty trees with perfect curves in perfect colours. Their swaying psychedelic splendour was designed to be low-maintenance and large-scale, and designed well. Patterned roots weed out any native plant for tens of metres around, and sapling-drones slink about on tendrils, electrocuting trespassers. Bones are plentiful here.

At the very edge of the waste lies the final graveyard: a dry reef, skeletons of coral and fish-armour still clearly visible high above the dust. It is beautiful in its own right, and a haunting reminder of what can be so quickly lost.
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[hider=The Waste]
There is little to see in the Waste. Former seafloor has become sand, and silt, and salt in enormous quantities. The hot, hypersaline oceans beyond raise heavy winds, and dust storms often join the clouds in obscuring visibility. The place alternates between desert and huge puddles of rainwater, a short-lived shadow of the ocean it once was.

Wrecks are visible every now and again, bits and pieces of spacecraft that broke up in orbit, and meteorites are common. Tall probes blink in the haze, their origin unknown. Whatever they're looking for isn't here. There's nothing to see.

Beyond, the continental shelf falls away into an ocean of acidic brine. Former sea platforms that once sat near the surface now tower high above it, some still inhabited. Self-sufficient colonies of hermits and the desperate have set up shop here, minding their own business as if they have any choice in the matter.
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[hider=West Sector: Shipwreck]
A downed spaceliner sits on an otherwise featureless part of the waste. Several kilometers long and bearing too little in the way of survivors or military hardware to be worth salvaging, it has been left to its own devices for decades, forming lakes in its belly and caverns in its limbs.

A substantial number of Cambria's invasive aliens fled from this craft when their food began to run short, and few ever returned. Pets, pot plants, live food, and other luxury species now wander the Plateau, often in much hardier feral forms. What remains are robots: technicians, assistants and labourers of every shape imaginable.

Most, of course, are inoperable or dead. But some are lively. Born of a miracle of science or accident, a single droid whose name is the Grandfather been tinkering with itself and others since the war began, bringing to life a sparse handful of cobbled-together sons. The family grows bigger and smarter year by year, struggling to build a stable life in the ruined mother ship.

Communication with the fledgling culture has proven difficult, as they are tetchy around outsiders and their creole has no reference point for translation. By night they are known to wander into the Plateau, seeking organic resources they can find nowhere else. Sometimes they leave gifts. Mostly they leave well alone, and expect to be done the same.
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[hider=The Last True Sea: Trench]
Off the northeast 'coast' of the Plateau lies a trench that, now that the seas around have evaporated, happens to form an effective natural rain trap. This has preserved both the water's depth and relative salinity at levels not too far from where they were originally. Much like the Plateau, the Last True Sea now forms a slowly dying oasis of life as it was before the war.

Near-perpetual cloud cover places a stark limit on the abundance of food, but the region is volcanically active and there is life enough around its many vents and seeps. Sometimes the melting nuclear cores of fallen ships perform the same function. Like long-legged caterpillars, spined hallucigenids crawl around the vents' encrusting sponges, which are familiarly bright and colourful. Wiwaxids and marellas creep about, displaying scales, blades and elaborate antennae, alongside trilobites with big shimmery eyes and long curly spikes. Many-eyed animals swim above with mouths on long stalks, looking to pick out a meal from the well-armoured swarms. It's a small world, but a beautiful one.

Beyond, rangeomorphs sway and ripple on the barren stone and steel, pale fronds many metres long, fractally grown organisms of the most ancestral kind imaginable. Blips no grander than a tiny disc of patterned jelly are the liveliest representatives of animalkind, and are complacently preyed upon by spriggs not yet complex enough to be called worms. Larger anomalies swim about, man-sized paddlers slowly sifting food from the brine. Like whales, they are the greatest beasts in the region, and like whales, they were the first to disappear.
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[hider=The Last True Sea: Reef]
Near the base of the Morass, where fresh water flows and mountains block the passage of the clouds, the sky is still bright. Below it blinks a thriving reef, the likes of which has survived well enough to grow over any wrecks that may have fallen here.

Corals, cyaths and algae form brilliant layers of living architecture, and sea lilies perch all around to flare their flowering tentacles. Some of these flowers are larger than trees, and give shelter to every kind of sea-beetle. With them live slug-like cephalopods in a tall witch's hat of a shell, creeping about and ducking away under their hats should an armoured fish swim by, perhaps migrating from the Morass above.

Both these little families have relatives with no need to hide. Long-tailed sea scorpions brandish pincers, spines and bristles on their powerful arms, and are more than large enough to tear through a diving suit. The cousins of the cephalopods grow larger still. A towering spike drifts by in the distance: slow it may be, but don't come too close, for it is curious and the tentacles below are not fragile.
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