From its source in the province of Ávila, to its mouth in the village of Pollos "("Village of Chickens" in Spanish)" in the Vallisoletana (""confluence of waters"") region, the course of the Trabancos is markedly affected by a geologic fault originating in the Tertiary era—likely pre-Pliocene that, like most of the observed faults of that geological era, follows a NNE-SSW direction. As shown in the graph below, the fault separates material laid down during the Oligocene epoch on the right margin, from material laid down during the Miocene epoch on the left margin. The surface level represents material deposited during the Quaternary period.