Yellow starthistle, Centaurea solstitialis, is a fast-growing annual herb from the eastern Mediterranean Basin that has invaded grassland in California and other western states. At Jasper Ridge Biological Preserve in northern California, starthistle grows on portions of the sandstone grassland, but is completely absent from the adjacent serpentine grassland. This study was designed to help determine the factors which affect yellow starthistle distribution. Several hypotheses have been suggested to explain the absence of starthistle on serpentine soil. The presence of heavy metals, low moisture content, and inadequate nutrient concentrations in serpentine are some of the more popular theories. I hypothesized that serpentine soil was drier and had lower concentrations of the nutrients potassium, phosphorus, and nitrogen than did sandstone soil. I also hypothesized that nutrient concentrations were equal in the sandstone soils with starthistle and without starthistle because they originate from the same parent rock, but that moisture content was higher in sandstone soil with starthistle. Potassium concentrations were found to be higher in the sandstone soils than in serpentine soil, providing a possible explanation for the absence of starthistle on serpentine grassland. Phosphorus concentrations were highest in serpentine soil, and moisture content and nitrogen concentration were equal across soil types. These three factors probably are not responsible for the absence of starthistle on serpentine grassland. However, because of unusually high precipitation in California this year and insensitive methods of determining nitrogen concentrations, it is possible that moisture content or nitrogen concentrations, or both, differ across soil types. The phosphorus concentration in sandstone soil with starthistle exceeded the concentration in sandstone soil without starthistle, a phenomenon which may help explain starthistle's distribution on sandstone grassland.