Looking beyond the lava and spatter in front of you, and just beyond the line of trees, can you see a reddish hill? This is an agglutinate mound or pile of welded pyroclastic material.
In the early stages of the eruption, a cone began to form next to a major explosive vent. The cone became armored by welded deposits. Then a column of dense magma broke through the base of the cone, causing the upper part of the cone to collapse onto the top of the flow. The slumped pieces were then rafted away by the flowing lava. You are looking at a large piece of an early-stage cone of Sunset Crater.
Perhaps within weeks or days after breaching, the cone was rebuilt, creating the symmetrical cone of Sunset Crater we see today. Any remnants of the earlier cone lie buried beneath tons of cinder.
Meghann M. Vance, Northern Arizona University Anthropology Laboratories