Despite accounting for only 1% of land cover in California, serpentine grasslands support 13% of the state’s endemic plant species. Although there have been many studies on the floral composition and structure of these grasslands, few have investigated the native small mammals that rely on this rare habitat type. We here study the dynamics of a small mammal community from a serpentine grassland at Jasper Ridge Biological Preserve in Woodside, California using barn owl (Tyto alba) pellets. 253 pellets were collected regularly between fall 2007 and summer 2008. From these pellets, at least 670 small mammal individuals from 9 species were identified from craniodental remains. We analyzed the trends in species abundances on two temporal scales: seasonal and monthly. When looking at seasonal changes the two most abundant species, Microtus californicus and Reithrodontomys megalotis, exhibited parallel fluctuations in abundance, peaking in the winter and declining through spring and summer. However, at the monthly scale we found negative associations in their abundance, which could stem from a competitive dynamic that was observed in previous studies in non-serpentine grasslands. Our study shows that this competitive dynamic is consistent across both serpentine and non-serpentine grasslands as well as emphasizes the importance of analyzing community dynamics at multiple resolutions.