The California Floristic Province is a well-known hotspot for biodiversity, containing more endemic species of plants and animals than any North American region of comparable size. This astounding diversity is partially a reflection of the complex geologic history of the region, which has shaped the evolutionary and biogeographic histories of endemic taxa. The harvestmen genus Calicina is represented by 25 California-endemic species, which occupy a disjunct distribution in the Sierra Nevada, Transverse and Coast Ranges. Species in the genus exhibit extensive variation in morphology, which is hypothesized to be correlated with differences in habitat. The first objective of this research was to infer a time-calibrated species tree for Calicina, using multiple genes and multilocus coalescent-based methods. This inferred phylogeny does not support previous hypotheses of species group and subgroup relationships based on genital morphology. The second objective was to reconstruct the historical biogeography of Calicina. Divergence time estimation and biogeographic analyses suggest three independent colonizations of the Coast Ranges, and two independent radiations along the Sierra Nevada: in the foothills, and along the higher-elevation coniferous forests. This vicariance-dominated biogeographic history is coincident with the geologic evolution of California since the mid-Paleogene. The third objective of this research was to examine the relationship between paedomorphic morphology and climate. Bivariate and multivariate comparative analyses recover a relationship between paedomorphic morphology and environmental variables, indicating a strong association of climatic variation with morphological evolution in Calicina.