Nemegtomaia is known from the Nemegt and Baruungoyot Formations, which date to the upper Campanian-lower Maastrichtian ages of the Late Cretaceous period, about 70million years ago. Though this taxon is known only from the Nemegt locality, unidentified oviraptorid remains from other localities may belong to it. The Nemegt massif has numerous canyons or gorges, up to deep, which have some of the best exposures of these formations. The rock facies of the Nemegt Formation are thought to represent a humid, fluvial (associated with rivers and streams) environment, whereas those of the Baruungoyot Formation are thought to represent an arid or semi-arid environment, with aeolian (affected by wind) beds. These two formations with their diverse fossils were historically thought to represent sequential time periods with different environments, but in 2009 the Canadian palaeontologist DavidA. Eberth and colleagues found that there was partial overlap across the transition between them. The two formations interfinger across a stratigraphic interval that is about 25 m (82 ft) thick, which suggests that the fluvial and aeolian environments coexisted when the area was sedimented.