Hot winds fueling a massive wildfire that prompted evacuations in rural Northern California have pushed the flames into three counties. The California Department of Forestry and Fire Protection said Monday that the blaze that ignited Saturday in western Yolo County spread over the weekend to neighboring Lake and Napa counties.

The fast-moving fire has scorched at least 55 square miles of dry brush and threatened more than 100 buildings in ranchland northwest of Sacramento. No injuries were reported and the exact number of people evacuated was unclear. Smoke and ash are contributing to poor air quality in the San Francisco Bay Area and California wine country. Hot, dry conditions are also fueling blazes in several other Western states.