A transect of infusion-baited oviposition tubs was used at the Orange County (CA) Vector Control District facility to determine the circadian periodicity and the influence of urban habitat factors, such as buildings, ornamental plantings, and mercury vapor lights on Culex quinquefasciatus oviposition activity. The peak oviposition activity occurred during the first 2 h after sunset. Nearly 80% of egg rafts deposited were laid within the first 4 h after sunset and no morning ovipositional peak was detected. Urban and physical habitat factors considered had no effect on tub selection by ovipositing females. Linear analysis indicated that eggs were laid randomly among tubs. Eighty-eight percent of the rafts collected were Cx. quinquefasciatus. The remaining egg rafts were laid by Culex tarsalis, Culex stigmatosoma, and Culieseta incidens.