"Tartaria" is a fantasy based on misconceptions and ignorance.
When the mongols started their expansion under Genghis khan they subjected many turkic tribes called tatars - not "tartars". These pastoral horsemen were a crucial part of the mongol army, and because all of the pastoral people from central and north asia were indistinguishable for contemporary europeans and the tatars reminded them of "tartaros", the greek underworld. The name "tartar" got stuck, and "tartaria" was used as an umbrella term for all home areas of those asian pastoral peoples. In the early 1800s "tartaria" was already part of the russian empire, but neither the russians nor any of the siberian people have a lore of a cataclysmic event - and if there was a technological advanced civilisation one would expect at least the tatars to know about it. Strangely that's not the case.
In addition they had close cultural ties to other cultures, especially to china, mongolia, persia and the ottoman empire. But none of those cultures with a great interest in historiography and diplomacy has any knowledge of "tartaria".
Interestingly enough that of all places in "tartaria" no alleged "tartarian" architecture can be found - but this can't be caused by the claimed cataclysmic nuclear war because the area is so damn huge that a nuclear annihilation of such a magnitude would have destroyed the world as a whole. Not just 3 cold years but a full blown nuclear winter for decades.
"Tartaria" is one of the most ridiculous conspiracy theories, and any person with half a brain could figure out that it's just a fantasy within 3 minutes.
"Tartaria" goes often hand in hand with the mud flood conspiracy which is even more outlandish. If I wouldn't know better I would think it was a parody of a conspiracy theory, but unfortunatly it isn't.