Here, we explore variation in a new record of archaeological house-floor sizes from the southwestern United States relative to spatially explicit time series estimates of local precipitation. Our results show that inequality becomes more severe during periods of high precipitation. This supports the theory suggesting that inequality may emerge where resources are dense, predictable, and clumped within heterogenous and circumscribed environments. Our findings indicate that wealth inequality may emerge among populations with similar subsistence adaptations as a result of local socioenvironmental variation.