National assessment of soil carbon across the U.S. has been based on legacy data (Soil Survey Geographic Data – SSURGO and State Soil Geographic Data – STATSGO), which have become outdated due to global climate and land use changes, and human induced disturbances imposed on soil carbon dynamics in soil ecosystems. We present a new soil carbon stock assessment using recent extensive sampling (1 m depth) at several thousand sites in different soil and land use types. We assembled space-time sequences of environmental covariates covering the U.S. from various sources (remote sensing, such as the Moderate Resolution Imaging Spectroradiometer, MODIS; National Elevation Data; temperature and precipitation from PRISM project, etc.). The characterization of soil organic and inorganic carbon stocks along lithologic, pedogenic, topographic, biotic, and climatic trajectories provides new insight into causes and effects of soil carbon accretion. In the U.S. climate change has varied profoundly spatially and temporally over the past decades. Here we present the forcings of short- and long-term climatic change on the formation and distribution of soil organic carbon within different biomes and ecoregions in the U.S. The modeling of soil carbon variation within a spatially and temporally explicit modeling framework that incorporates environmental covariates offers a new perspective on the state of knowledge on soil carbon variation in a landscape stretching over diverse climatic zones (from semiarid to wet tropical) and biomes.