Cover Image: Confluence of the Rio Embudo and Rio Grande
— Paul Bauer
Confluence of the Rio Embudo and Rio Grande in the Rio Grande Gorge, looking upstream (towards the east). Photo courtesy of Paul Bauer. The gorge formed due to net incision of the Rio Grande during the late Pliocene and Pleistocene. The lead article of this volume uses dated basalts to interpret the river’s history between 5.5 and 4.5 million years ago, prior to the development of the gorge. During that time period, two merging tributaries to the ancestral Rio Grande deposited a 10–25 m-thick package of gravelly sand as far as 14 km northeast of the present-day course of the river.