The purpose of this assessment probe is to elicit students’ ideas about the formation of the Grand Canyon and is specific to the Grand Canyon. The probe is designed to find out if students recognize the role of rivers and flowing water and connect them to the processes of weathering and erosion in the formation of canyons. Although several factors contributed to the formation of the Grand Canyon over a long period of time, the primary processes responsible for the canyon we see today are weathering and erosion by river systems. This probe is best used with grades 3–8, and can be extended by asking students to describe a model they could use to explain how the Grand Canyon was formed. A materials list, teacher background information, references, assessment, and outcomes are provided. This book selection includes the Table of Contents, Foreword, Preface, Acknowledgments, About the Authors, Introduction, and Index.