The Colony and Paradise fires, ignited by lightning strikes last week, covered about 11 square miles (28 square kilometers) in California's steep Sierra Nevada.
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The Colony Fire was a threat to Giant Forest, home to more than 2,000 sequoias, but not imminently, said Mark Ruggiero, fire information officer for Sequoia and Kings Canyon national parks.
The fires are among the latest in a long summer of blazes that have scorched more than 3,500 square miles (9,065 square kilometers) in California, destroying hundreds of homes.
Sequoia National Park has been closed and its headquarters and resident employees have been evacuated, along with a portion of the community of Three Rivers outside the entrance.
The park's historic wooden entrance sign dating to 1935 was covered in fire-resistant wrapping, and hoses were in place at the headquarters area for structure protection.
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More than 300 firefighters were on the lines, aided by helicopters and air tankers when smoke conditions allowed. On Thursday, a national interagency management team will take over the fires, being managed collectively as the KNP complex, and even more resources are expected, Ruggiero said.
A 50-year history of using prescribed burns to remove other types of trees and vegetation in the park's sequoia groves was expected to help the giants survive by lessening the impact if flames reach them, Ruggiero said.
Giant sequoias, some thousands of years old, live on the western flank of the Sierra. They are adapted to fire, which can help them to thrive by releasing seeds from their cones and creating clearings that allow young sequoias to grow.
But Ruggiero noted that the extraordinary intensity of fires in current climate conditions can overwhelm sequoias, a scenario that played out when the 2020 Castle Fire killed many trees in the region.
Studies estimate that 7,500 to 10,600 large sequoias were killed by that fire, along with many of other sizes, according to the National Park Service.
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The Colony Fire also poses a broader danger because it is burning at an elevation of the central Sierra where there are 280 million pines and other types of trees that have been killed by drought and bark beetles, Ruggiero said.
"The Colony Fire specifically is burning in a really bad spot ... where these trees are like jackstraws and it's difficult to put fire personnel into some of these areas because of that," he said.
Elsewhere, two California fires that have caused extensive destruction in the northern Sierra and southern Cascades were not growing.
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The state's second-largest fire on record, the Dixie Fire, remained 75% contained after burning 1,500 square miles in the northern Sierra and southern Cascades region. Near Lake Tahoe, containment of the 342-square-mile (885-square- kilometer) Caldor Fire increased to 70%.
North of San Francisco, a 20-year-old Ukiah man was arrested Tuesday and jailed on suspicion of starting the Hopkins Fire in Mendocino County, the California Department of Forestry and Fire Protection said in a statement. The fire that sparked Sunday north of Ukiah charred 257 acres (104 hectares), destroyed homes and forced evacuations.
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