Soil properties are known to have a profound effect on the geographic distribution of plants. Unusual soils seem to allow species to occur outside their ‘typical’ (realized) climatic niche. However, the generality of this pattern, and the mechanisms that drive it, are poorly known. Here, we focus on the tendency for some plant species to occur at unusually low elevations on infertile substrates, especially serpentine soils. We ask whether there is a flora-wide trend in the state of California toward lower elevations and warmer thermal limits on infertile serpentine soils than on other soils.