At the southernmost end of the Northern Cordilleran Volcanic Province, Tseax Cone lies in a valley above and east of the Tseax River. It is a young Holocene age cinder cone that was the source for a major basalt lava flow eruption around the years 1750 and 1775 that travelled into the Tseax River, damming it and forming Lava Lake. The lava flow subsequently travelled north to the Nass River, where it filled the flat valley floor for an additional , making the entire lava flow long. Native legends from Nisga'a people in the area tell of a prolonged period of disruption by the volcano, including the destruction of two Nisga'a villages known as Lax Ksiluux and Wii Lax K'abit. Nisga'a people dug pits for shelter but at least 2,000 Nisga'a people were killed due to volcanic gases and poisonous smoke (most likely carbon dioxide). This is Canada's worst known geophysical disaster and is the only eruption in Canada for which legends of First Nations people have been proven true. As of 1993, the Tseax Cone quietly rests in Nisga'a Memorial Lava Beds Provincial Park.