Stabilization of organic matter on mineral surfaces strongly affects rates of soil organic matter (SOM) accumulation and turnover. Controls over SOM are of particular interest in arid and semi-arid systems where the abundance of woody plants has increased globally over the past century. This proliferation of woody plants may lead to significant soil organic carbon (SOC) accumulation, although a large degree of uncertainty exists in the direction and magnitude of SOC pool responses to woody encroachment. We hypothesized that SOC accumulation from woody encroachment would be primarily due to increased light fraction C pools and also that soil parent material would strongly influence SOC stabilization. Previous studies at mesic sites have used sequential density fractionation to separate soil particles based on mineralology and to explore C stabilization via organo-mineral complexes that might affect particle density. We explored mechanisms of SOM stabilization in arid soils by density fractionating four Chihuahuan Desert soils. The soils differed in parent material (igneous vs. limestone alluvium), landscape position (bajada vs. basin floor), and dominant vegetative cover (intact grassland vs. shrubland in former grassland). We used sodium polytungstate to separate soils into seven fractions with density cutoffs of 1.68, 1.87, 1.98, 2.18, 2.47, 2.66, and >2.66 g cm-3 (hereafter F1-F7, respectively). Concentrations of C and N generally decreased with increasing particle density. Similar to findings from mesic sites, C:N decreased with increasing particle density. While F1 accounted for a small proportion of total mass (0.29-2.61%), a large proportion of total C was present in this fraction (25.3-39.2% of total) due to the high [C] (21-38%C). Carbon in these light fractions is likely to be primarily recently-derived plant material that turns over rapidly and is not stabilized on mineral surfaces. The basin floor sites contained a large proportion of the total C in F5 (38 and 52% of total) despite relatively low [C] in this fraction (1.2 and 1.0%C). In contrast, the bajada sites had similar [C] in F5 (1.0 and 1.2%C), but a lower proportion of total C in this fraction (25.8 and 21.9% of total). Contrary to our expectations, C and N pools in both bulk soils and density fractions were largely consistent among soils within the same landscape position, while neither dominant vegetative cover nor parent material strongly influenced C and N distribution among density fractions.