INTRODUCTION

Charles A. Repenning, during the last years of his life, took an active interest in issues that surrounded the archaeological investigations at the Valsequillo Reservoir, south of the city of Puebla, Mexico, where four separate sites had been located (Figure 1). Thus, he corresponded with paleontologists who had preceded him, and he studied all written aspects about the archaeology and geology. Repenning brought to Valsequillo his vast knowledge of Pleistocene geology and paleontology. At the time of Repenning's death, many of the Valsequillo issues that concerned him were incompletely understood and remain unresolved. Also, new investigators with new interests have begun to study the sites. Therefore, we judge it fitting to offer this brief history of past and current work at Valsequillo as a tribute to Repenning and his scientific efforts on our behalf.

Significant among current scholars with an interest in Valsequillo is a British group headed by S. González of Liverpool John Moores University, UK. González and her associates, based on their work since 2003 and published reports that date from 1957, put forward their digest of the archaeological discoveries at Valsequillo (González et al., 2006). They asserted that the artifacts and associated megafauna are reworked, not indigenous (in situ) to a widespread geologic unit called the Valsequillo Gravels, as described by the original investigator, C. Irwin-Williams (1967a, 1978; Irwin and Armenta Camacho, 1963). They further reported a new chronology of the stratigraphy, founded on the premise that a unit of basaltic ash, known as the Xalnene tuff, which underlies the Valsequillo Gravels, is about 40,000 years old, not 1.3 Ma, as previously reported by Renne and others (Renne et al., 2005; Feinberg et al., 2009). Our stratigraphic work at Hueyatlaco, the principal archaeological site at Valsequillo, is described here. It supports the older chronology. An earlier comprehensive history of the Valsequillo investigations was presented by Hardaker (2007).