Observations of aerosol physical, chemical, and optical properties made at 38 locations in Washington, Oregon, and California are presented to show the regional-scale influence of wildfire smoke during the summer of 2002. Aerosol measurements made during an intensive field campaign conducted in July, August, and September 2002 in Yosemite National Park indicated that smoke-impacted aerosols were present at the park during frequent haze episodes. In addition, backward trajectory analyses showed that large-scale meteorological conditions during the study were dominated by transport from western and southern Oregon, a region with high fire activity during the summer of 2002. Observations of aerosol properties at the Yosemite NP site were remarkably similar, with similar temporal variations, to data from a second monitoring site at Blodgett Forest Research Station in the Sierra Nevada, approximately 150 km to the NNW. Further similarities to the temporal changes in aerosol properties as measured by monitoring networks with numerous sites in California and Oregon confirmed the regional nature of the haze, which had elevated fine aerosol particle mass concentrations compared with typical summertime average concentrations. The observations suggest that emissions from wild fires can have strong and sustained regional impacts on aerosol concentrations, air quality, and visibility.