The Contreras Fire burning in southern Arizona has grown to 20,360 acres, prompting possible evacuations for nearby residents, officials said.

While an evacuation hasn’t been mandated, the Pima County Sheriff’s Department said in a news release early Monday that residents of the Hay Hook Ranch Estates area “should consider voluntarily relocating outside the affected area with family/friends.”

The department reminded residents to “keep in mind” the items they might need to for pets and livestock, and to stay updated on the latest fire news.

“Emergency services cannot guarantee they will be able to notify everyone if conditions rapidly deteriorate,” the department said.

The fire, burning roughly 40 miles southwest of Tucson, is 40% contained, according to InciWeb, a US clearinghouse for fire information.

On Friday, the Contreras Fire damaged several buildings at the Kitt Peak National Observatory, the National Science Foundation’s NOIRLab (National Optical-Infrared Astronomy Research Laboratory) said in a release.

“All physical scientific observatory structures are still standing and in the case of the facilities on the South West ridge there is little visible external damage at this time; however several non-science buildings were lost,” NOIRLab said.

The fire is burning in highly flammable grass and brush in steep, rugged terrain that is difficult for firefighters to access, according to InciWeb.

The blaze began June 11 on a remote ridge of a mountain range on the Tohono O’odham Indian Reservation, InciWeb says. It lists the cause as lightning.

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