Critical zone processes contributing to soil development over the contrasting bedrock parent materials in the Luquillo Mountains has resulted in significant differences important to organic C quantity and soil organic matter (SOM) quality. Similar vegetation cover at sites on contrasting slope positions or underlying lithology will likely generate similar surface litter. Once this litter enters the soil, however, we ask: 1) will the resultant SOM be chemically distinct or is it simply protected differently? and 2) how do slope position and lithology alter the depth distribution and quality of organic C?