The Finlay tephras are largely composed of elements most similar to those of Hoodoo Mountain, a flat-topped volcano that formed subglacially at least 100,000 years ago. Two phonolitic lava flows on its south flank were erupted between 10,000 and 9,000 years ago and remain unglaciated. They have a similar chemistry to the glass composition of the Finlay tephras. However, no tephras or pyroclastic rocks have been found at Hoodoo Mountain that were erupted the same time as these lava flows. Therefore, other possible sources have been proposed. At the Mount Edziza volcanic complex, basalts of probable Late Pleistocene to Early Holocene age have been found, but their exact ages and chemical compositions are not well known. Because Heart Peaks and nearby Level Mountain have been poorly studied and it is unknown if they contain Holocene age volcanic rocks, they are also possible sources for the Finlay tephras.