A woman was arrested after she told firefighters that she had intentionally set fires that became part of a larger blaze that is still burning along the border of California and Nevada, the authorities said Tuesday.

The woman, Christine Mitchell, 47, was arrested on suspicion of third-degree arson and possession of less than 14 grams of a controlled substance, the Washoe County Sheriff’s Office in Nevada said in a statement on Tuesday. Ms. Mitchell’s public defender didn’t respond to a request for comment.

Ms. Mitchell left a home near Freds Mountain Road and set multiple fires, the sheriff’s office said. She caught the attention of firefighters who were responding to the resulting blaze, known as the Fred Mountain fire, and told them she had meant to start the fire.

The Fred Mountain fire, which is burning north of Reno, Nev., has since merged with another nearby wildfire, known as the Bug fire. The Bug fire, which is 3 percent contained, has covered more than 70,000 acres and has forced thousands of people to evacuate, including from tribal land. It’s one of many large wildfires burning in the western United States during a fire season that has been unusually active for much of the region.

Ms. Mitchell was taken into custody on Sunday. Senior Judge Derek Dreiling at the Reno Justice Court set her bail at $80,000 on Tuesday, according to court records.

The sheriff’s office did not explain what the authorities believed Ms. Mitchell’s motive might have been for starting the fires.

The Reno-Sparks Indian Colony declared an emergency in response to the fires, and its Hungry Valley community was evacuated. Another large blaze east of the Bug fire, called the Stallion fire, is threatening Pyramid Lake Paiute tribal land. The Stallion fire, which officials said was caused by a human, was not contained as of Wednesday morning.

“We understand our Hungry Valley residents are frustrated,” Bethany Sam, a spokeswoman for Reno-Sparks Indian Colony, said during a Facebook livestream Tuesday night. “We know you all want to come home, check on your property, take care of your animals and get back to your normal lives.”

Gov. Joe Lombardo of Nevada also declared a state of emergency on Monday, citing a shortage of wildland fire resources as several wildfires burned across the region.

This week, the Federal Emergency Management Agency authorized the use of federal funds to help Nevada fight the fires.

Kirsten Noyes contributed research.