The last time it was this dry in January, there were barely more than 500 people in San Diego. The year was 1850, and only a quarter-inch of rain had fallen in six months. It made the region ripe for wildfire — but that wasn’t much of a concern. The city’s population was clustered along the coast, far from the backcountry, where most fires burned.

The fires come as San Diego County mountains and valleys, along with other parts of Southern California, remain under a red flag warning.

A critical fire threat will continue across County as Santa Ana winds and dry conditions persist through early Friday, according to the National Weather Service.