prompted a red-flag warning, meaning conditions are favorable for the spread of wildfires. the warning affects about 6 million people, and it includes that dixie fire which has already burned an incredible nearly a million acres. crews are also battling a fire that has reached sequoia national park. it's an area where some of the world's largest trees have stood for thousands of years. cnn's stephanie elam is covering that part of the story. >> reporter: from their size, general sherman is 275 feet tall. holy cow. to their longevity. >> before ancient rome, before christ, i mean, these trees were -- were mature. >> reporter: much about giant sequoia trees is on a grand scale. with that distinctive, red-brown bark covering their thick trunks, sequoia trees can only be found in california's sierra nevada mountains. >> this is a resilient tree.