The anthropogenic increase in atmospheric carbon is partially mitigated through afforestation. However, the role of soils in the forest sink is poorly understood. This study was conducted to determine the rates of soil carbon accumulation and transformation during early stages of pedogenesis under semi-arid coniferous forest. The chronosequence used for this study consists of a series of debris flows in the San Bernardino Mountains, which range in age from <1 year to 400 years. Conifer stands, of mostly ponderosa pine and incense cedar, are established in the first year after a debris flow and were used to date the flows by dendrochronology. A resolution of ~10 years was established for the past hundred years, with fewer preserved flows back to 400 years. Pedon description and sampling according to morphologic horizons (or defined depths where horizons have not formed) was conducted at each stage of the chronosequence. Pedogenesis in this chronosequence is driven mainly by organic carbon from the growing forest biota. The highest rates of carbon accumulation occur during a period from 30-100 years after the debris flow, during which time morphologic influences of the carbon accumulation are seen in the deepening A horizon with decreasing bulk density. Slower processes, including accumulation of carbon in residual forms associated with the clay fraction, melanization of the surface soil, and incorporation of carbon in the lower profile, occur throughout the chronosequence. This high resolution chronosequence provides a detailed record of the initial stages of soil development.