A nearly 40,000-acre wildfire forced people from their homes in two Southern California counties over the weekend as firefighters worked to contain the blaze in challenging terrain.

A wildfire sparked Sunday afternoon in Clearlake has spread to about 100 acres within an hour, triggering two evacuation orders, according to fire officials.

The Gifford fire has rapidly spread after firefighters contained the Madre fire. Together, the two blazes have already burned over 100,000 acres.