Clarkia tembloriensis and "Caliente" (an undescribed Clarkia species) in a low elevation grassland habitat flower about 2 weeks earlier than sympatric or adjacent populations of C. unguiculata. At higher elevations in a woodland habitat C. exilis blooms later than the lowland populations, but about 2 and 4 weeks earlier than adjacent populations of C. unguiculata and C. xantiana, respectively. Time of flowering is differentially correlated with, and interpreted in terms of adaptation to, the onset of summer heat and drought.