Tallahassee Creek Conglomerate and Echo Park Alluvium
Prior to the eruption of the Wall Mountain Tuff, some valleys in the region were filled with eroded rocks and debris from the surrounding mountains, named the Echo Park Alluvium. Over 2 million years passed between the deposition of the Wall Mountain Tuff and deposition of the volcanic material into the ancient lake at Florissant. During that time, much of the Wall Mountain Tuff was eroded away, leaving only scattered outcrops of its once immense lateral expanse. In place of the now-eroded Wall Mountain Tuff, the Tallahassee Creek Conglomerate was deposited along the valley.