For more than 150 years, scientists have debated when and how the Colorado River first carved its way through the Grand Canyon. Now, a new study led by researchers at The University of New Mexico offers compelling evidence that the river developed gradually from north to south between 8 million and 4.8 million years ago. Published in Nature Communications, the study, “Tectonically driven integration of the 4.8 Ma Colorado River USA,” tracked with detrital sanidine and fish genetics, combines geological dating techniques with fish genetics to reconstruct the river’s ancient history. Rather than forming through a single catastrophic event, the researchers found that the Colorado River emerged as a series of smaller proto-rivers gradually linked together over approximately 3 million years.