The Rocky Mountain Region has been the subject of continuous, exhaustive scientific work since the first organized geologic trips to the area began in the 1860s. Despite almost 150 years of scrutiny, the region's magnificent geology continues to challenge, perplex, and astound modern geoscientists. It is a testing ground for geologists and for big geologic ideas. This volume, prepared for the 2013 GSA Annual Meeting in Denver, Colorado, serves both as a progress report on what we have learned over those years of study and a guide to forthcoming scientific questions about the region. The guide's fourteen chapters, which span the region's 1.7-billion-year history, give a retrospective glimpse of early geologic ideas being forged, bring the latest mapping and analytical results from classic locations, and introduce techniques that will form the bedrock of our geologic understanding in the years to come.