High-level terraces in the Indian River valley, between the confluences of Ruby Creek and Dominion Creek with Indian River, are underlain by a sand-dominated fill. The fill formed when meltwater torrents from the margin of a Late Pliocene ice sheet drained into the Indian River valley from the divide with the Stewart River basin. A lake or lakes existed in the Indian River valley at that time. Mechanisms for ponding of the lake(s) include regional glacial damming of the ancestral Yukon drainage (Glacial Lake Yukon), or local damming by alluvial fans or landslides. Sufficient evidence does not exist to effectively eliminate any of these hypotheses. Placer gravel may exist below the sandy fill in a buried segment of the pre-glacial Indian River valley near the confluence of Montana Creek.
