Abstract: With climate change, heat waves (HWs) are predicted to increase, particularly in areas where HWs have historically occurred. A multitude of studies have demonstrated that human mortality increases during HWs. California has suffered a number of HWs. The "Great" California HW of July 2006 was unprecedented in duration and occurred statewide, lasting ten days in much of the state and longer in some areas. We calculated the ratio of deaths during the heat wave period (July 15 – Aug 1, 2006) to deaths on non-heat wave days in the same summer. We calculated these rates by California\'s sixteen building climate zones. These zones were outlined in 1982 based on climate, elevation, and estimated energy consumption. HW mortality ratios were higher: i) in the northern coastal zone (a 19% excess of mortality) compared to other coastal zones ofCalifornia (-0.1 to 6% excess); and ii) in the southern and northern zones of the Central Valley (a 11 to 12% excess) compared to the central zone of the Central Valley (a 2% excess). We examined available meteorological, census, and other data, and discuss whether these differences may be related to zonal differences in HW intensity or duration, air conditioning use, building insulation requirements, or other factors such as occupation. Notably, the northern and southern zones of the Central Valley are farming areas. In contrast, the central zone of the Central Valley includes the state capitol, where a higher percentage of workers are office workers. Identifying resilient (low health impact) and vulnerable (high health impacts) zones, and factors that may mitigate the health impact, may ultimately inform climate change mitigation and adaptation policies.