High bedrock incision rates in the Atenguillo River valley, Jalisco, Western Mexico

Abstract

Lava flows from three basaltic shield volcanoes preserve Pliocene–Pleistocene river levels in the Atenguillo River basin, western Mexico. K–Ar dates of these basalt flows, together with present and palaeoriver levels, allow calculation of bedrock incision rates at three points along the length of the Atenguillo River: at Volcan La Laja, dated at 0·65 Ma, incision rates are 25 cm ka−1; at Volcan La Cienega (2·2 Ma) incision rates are 23 cm ka−1; and at Volcan El Vigia (2·7 Ma) incision rates are 23 cm ka−1. These high incision rates, as well as two distinct knickpoints along the profile of the Atenguillo River, are related to a base level c hange at the northern end of the basin. The dynamics of this river basin are controlled by the ongoing process of continental fragmentation associated with the opening of the Gulf of California. © 1997 by John Wiley & Sons, Ltd.