To assess the effect of urban land-use change on soil organic carbon (SOC), we compared SOC stocks of turfgrass and native cover types of the Baltimore and Denver metropolitan areas, which represent climatologically distinct regions in the U.S.  We hypothesized that the effect of introducing turfgrass will lead to higher SOC densities in the arid Denver area, whereas in the mesic Baltimore area there should be a reduction in SOC densities relative to native cover types.  Moreover, differences between residential turfgrasses will be less than differences between the native soils of each metropolitan region.  Within Baltimore, turfgrass had almost a 2-fold higher SOC density at 0-1-m and 0-20-cm depths than in rural forest soils, whereas there were no differences with soils of urban forest remnants.  Within Denver, turfgrass (> 25 years of age) had more than 2-fold higher SOC densities than in shortgrass steppe soils, while having similar densities to Baltimore turfgrass soils at a 0-1-m depth.  The amount of SOC in 0-20-cm depth also was similar, though the percentage of SOC (relative to 1 m) at this depth was higher in Baltimore (50%) than in Denver (35%).  By contrast, the native soils of Baltimore were almost 2-fold higher than the native steppe grass soils of Denver using SOC densities of remnant forest soils as representative of native soils in the Baltimore region.  These results supported the hypothesis that differences in SOC densities between different climatic regions would be greater between native cover types than between residential turfgrass soils.