The Washburn Fire, which started near the Mariposa Grove of Giant Sequoias, has burned more than 2,300 acres and remains only 25% contained as of Monday afternoon.
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Air officials are warning that the smoky air could move into the San Joaquin Valley overnight, so residents should protect themselves now.
Visitors to Yosemite were faced with an hour-long wait at the Highway 140 entrance gate, and a view of smoky skies blanketing many parts of the park.
"We are very sad, very sad for the nature, very sad for our American people, for this beautiful treasure of this national park of Yosemite," said Emmanuel Cirrodde, who was visiting from France.
Another pair of visitors, Micah Centanni and his girlfriend, just did the 16-mile hike to Half Dome on Sunday.
Centanni said smoke reduced visibility, and ash fell all over their camp.
"Today our entire tent, the top of tent, was filled with ash," he said.
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While there's the smoke and ash you can see, there are also particles that are basically invisible that can impact your health.
"As we see the smoke come into the Valley, we want residents to understand that really it's a risk until the fire is out," said Jaime Holt, Chief Communications Officer with the Valley Air District.
Holt said the weather has been pushing the smoke east, avoiding the San Joaquin Valley, but residents still need to take precautions.
"If we start to see those unhealthy levels of air quality in the Valley, we really want folks to take precautions and protect themselves from this smoke," Holt said.
Some precautions he advised - staying inside with your doors and windows shut, and running air conditioning and air purifiers with fresh filters.
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If you have any condition like asthma, emphysema, or COPD, you need to be especially careful, as the smoke will aggravate it.
Back at the Mariposa Visitor Center, workers are advising tourists to enjoy the park, but to just take it easy.
"Don't go to the hardcore hikes," said Jacob Hawley with the Mariposa Visitor Center.
Officials said if you can smell smoke and see ash, that's an indication that you are being affected by poor air quality.