The cross section of a small floodplain [Beaverdam Run, Cambria County, Pennsylvania] in the Appalachian Plateau was shown in excavations and borings for a dam. Deposits of vertical accretion, lateral accretion, lag deposits, channel fill, and colluvium fill the valley of an aggrading stream. Colluvium comprises almost 1/5 of the total valley fill and contains isolated lenses of vertical accretion. The colluvium built out from the valley side as the stream shifted laterally across the floodplain. Vertical and lateral accretion deposits may be sharply differentiated where exposed in a trench; the lateral accretion is composed of 70-75% sand size material and the vertical accretion of 35-60% clay size material.