PHOENIX (AP) — Firefighters across Arizona were working to gain ground Monday against massive wildfires that led to surrounding communities evacuating.

In the foothills and mountains outside of Tucson, the so-called Bighorn Fire spread to higher elevations overnight. The 23-square-mile (60-square-kilometer) blaze is only 22% contained, fire officials said. It's now burning heavier fuels, which crews say will lead to denser smoke.

Some of the roughly 630 personnel working on that blaze will focus on strengthening fire lines on Mt. Lemmon. Others will be on the blaze's north edge toward the town of Oro Valley looking for possible containment areas.

Crews are trying to keep the fire at bay from the areas of East Golder Ranch and Ventana Canyon. The Pima County Sheriff's Office on Sunday allowed residents who had been evacuated from the area of East Golder Ranch Drive and East Rollins Road to return. But they are urged to stay vigilant in case evacuations are enforced again.