The foreground hills are part of the Shasta Valley debris-avalanche deposit produced by one of the largest known Quaternary volcanic landslides. Roughly 46 cu km of an ancestral Mount Shasta collapsed about 350,000 year ago, producing a massive debris avalanche that swept some 50 km to the north, filling the broad Shasta Valley with hummocky debris.
The hilly topography in the foreground is part of the massive debris-avalanche deposit produced by collapse of Mount Shasta. The roughly 46 cu km, highly mobile debris avalanche swept some 50 km to the north. The hummocky area represents relatively intact segments of the volcano that were carried within a more fluid matrix facies of the avalanche. Individual hummocks range up to a few hundred m in height and roughly 1 km in length.