The TT-3 platform features a very compact and thick Miocene epoch conglomerate formed of river-smoothed pebbles of quartzite, most likely cut by the Trabancos River ages ago, and cemented together by chalk and sandstone materials. While this Miocene conglomerate emerges from the banks of each river terrace, the quartzite in the conglomerate on the TT-2 platform, just northwest of the municipality of Siete Iglesias de Trabancos, likely derives from the action of the Duero River rather than the Trabancos River, as a slope in the terrain is thought to have caused the formation of an alluvial fan that deposited quartzite on the fluvial fossil river bed of the Trabancos.