Abstract: Previous studies have hypothesized that terrestrial sedimentation can constitute a sink for about 1 Pg C yr-1 globally. But, there is no consensus on whether soil erosion results in a net source or sink to/for atmospheric carbon dioxide. Relatively little is known about stocks, fluxes, and stabilization mechanisms of soil organic matter (SOM) in erosional and depositional settings. In this dissertation research. I examined (a) why and how soil erosion can constitute a C sink, (b) whether the criterion necessary for erosion to constitute a C sink is satisfied; and, (c) if the mechanisms that regulate SOM stabilization are different in eroding slopes compared to depositional settings of an undisturbed watershed. I determined, tested or inferred (1) stocks and stability of SOM associated with bulk and density/physical fractions of surficial and buried soils (using elemental- and radio-carbon analyses); (2) in situ and ex situ decomposition rates of organic matter (using litterbags and laboratory incubation); (3) the soil's overall chemical protective capacity (using proxies for concentration of crystalline primary, poorly-crystalline, and organically-complexed iron and aluminum in the soil): and, (4) biochemical composition and potential transformation of eroding and deposited C (using 13C-nuclear magnetic resonance). I found that, compared to eroding slopes, depositional basins: (a) accumulate up to three times more C; (b) reduce rate of eroded/deposited SOM decomposition; and (c) develop different mechanisms for eroded/deposited SOM stabilization. Consequently, I conclude that the main reason soil erosion and deposition constitute a net C sink is that erosion (and deposition) can reduce oxidation of soil organic matter by removing it from the near surface soil environment, making it inaccessible to decomposer communities (by burial and aggregation), resulting in changes in microclimate (especially increased moisture and reduced aeration in relatively flat alluvial/colluvial plains), and subsequent development of organic matter-mineral associations.