CHALCO, the Basin of Mexico Drilling Program, targeted the Lake Chalco sediment in the Valley of Mexico. Scientists drilled about 1,250 meters of lake deposits and recovered roughly 1,000 meters of sediment cores, aiming to recover a continuous ~500-meter sequence that could span about 800,000 years of North American climate. This would provide a rare, long climate archive—potentially becoming a standard reference sequence for studying climate history across the Americas. The sediments also hold records of the region’s tectonic shakeups and volcanic eruptions, helping researchers connect climate shifts with earthquakes and lava events in the Valley of Mexico. By analyzing the cores, scientists hoped to reconstruct past temperatures, rainfall, lake levels, droughts, and volcanic activity, improving our understanding of how climate and hazards shaped this densely populated region. The project, conducted at a site near Mexico City and completed in 2016, recovered most of the drilled material and stored the cores at the University of Minnesota for detailed study by an international team.