If any at all of these 'Tartarian' cities, structures, exhibitions, canals and populaces etc across N.America were already extant in 1800, would not the 1804 Lewis and Clark expedition, 1806 Pike expedition, the 1838 US Exploring expedition, the Amerindians, French, British, Canadians, Mexicans, Dutch and Spanish have somewhere referred to them in their records...

Lewis & Clark/Pike/US Exploring expeditions