These multipurpose structures absorbed water during heavy rains and released it during dry seasons, creating a water management system that prevented both flooding and droughts. For years, researchers have debated whether the immense work was built through top-down social organization at the direction of elite leaders, or if people could have collectively labored to construct it through bottom-up organization. Now, a team of scientists has used satellite imagery to map a 1,200-acre patch of the system in unprecedented detail. With that sample, they built a model to estimate the population and labor costs of construction in that area. But some of the smaller ridge structures could have been built by a single family over the course of a few days.