This year, 26 wildfires have already raged along the 2,600-mile (4,265-kilometer) Pacific Crest Trail, which runs through California, Oregon and Washington and has long been considered one of America's most spectacular hiking trails.
The fires have closed 16 sections of the trail, and hikers are scrambling to arrange a route around those sections.
Father-son duo Thijs Koekkoek, 52, and Taime Teesseling, 17, spent four months hiking the route this year, from Southern California to the Canadian border. In July, they had to cut their hike short and take a ride around the Shelly Fire near Etna, California. After additional fire closures further north, the pair ended up skipping about 400 miles of the route.
"There was no other way," said Teesseling, who lives in Amsterdam. "Otherwise we would have had to walk around it in the smoke and we didn't want to put ourselves in danger."
Since 2018, nearly 1,700 miles of the Pacific Crest Trail have been temporarily closed due to fires, according to Chris Rylee, a spokesman for the Pacific Crest Trail Association. Nearly 250 miles of the trail have burned.
Wildfires and the burns they cause have made parts of the trail more dangerous and forced hikers to close quickly. For hikers who venture further afield, the fires change their targets and become witnesses to dramatic environmental change. Meanwhile, when fast-moving wildfires strike, many rural communities along the trail are responsible for helping vulnerable hikers.
"The fire season is getting longer, less predictable, and affecting more trails, more trail users, and more trail communities," Rylee said.
The PCT, the West Coast's longer, more demanding answer to the Appalachian Trail, runs through the Mojave Desert, the Sierra Nevada and the Cascade Range. Between 6,000 and 8,000 people apply for permits from the trail association each year to hike long distances. Hundreds of thousands more visit the trail for shorter hikes.
But severe wildfire seasons have transformed the landscape, fueled by extreme temperatures caused by global warming, combined with more than a century of aggressive fire suppression that has created unhealthy forests.
According to John O'Brien, a California climate scientist who grew up near the trail and hikes it regularly, the signs of climate change are now clearly visible on the PCT.
"It's a long-term journey through climate history," O'Brien said.
In addition to the fire hazard, climate change is making water increasingly scarce in some areas along the route. Glaciers are retreating in the high mountains, often exposing slippery rock surfaces. Rivers often reach their peak flow earlier in the season, making crossings at these times dangerous.
Koekkoek and Teesseling said fire wasn't the only extreme weather they faced. In Julian, California, a heavy late-season snowfall forced them to take shelter. Then the two endured a week of nearly 100-degree heat near Burney, California, even at high elevations.
They said the locals they met kept repeating the same refrain: "We've never seen weather like this before."
The walk gave the father and son a crash course in how wildfires change daily life in remote, fire-prone communities, particularly in California: "Everyone had an emergency bag by the front door, and everyone had to be ready to leave their house," Teesseling said.
PCT hikers also need to be alert: when fires break out, they are among the most vulnerable. Many prepare for their hike with the assumption that they will skip sections of the trail because of fires, or "flip-flop": return later. Others try to string together complicated detours.
Karen Altergott, a 2022 hiker, was forced to leave the trail near Stehekin, Washington, after developing a nasty cough, headache and sore throat after three days of hiking in the smoke.
"My lungs were full of fluid," she said. This year, Altergott returned to complete her missing miles, ending up walking 17 miles in an N95 respirator. Then another fire left her 30 miles short of completing her mission, and she longed for closure.
"A part of me stayed there," Altergott said. "I firmly believe that it is now impossible to hike the Pacific Crest Trail without being affected by wildfires."
The Pacific Crest Trail Association launched a smartphone app this summer that helps hikers track and navigate the frequent and confusing wildfire closures.
"Trail angels" - locals who provide free food, support and sleeping places to hikers covering long distances - are increasingly playing a vital safety role by chauffeuring stranded hikers around due to fire closures.
"They're literally walking around with their lives," said Becky Wade, who along with her partner Jeff McCabe serves as a trail angel in Hamburg, Calif. "They have no way out unless you stop and help them."
McCabe and Wade moved to the area four years ago, near the Klamath National Forest. Wildfires have forced them to evacuate twice. Both times, they welcomed long-distance hikers and guided them to safety.
In July, McCabe transported about 75 hikers around the Shelly Fire, including Koekkoek and Teesseling.
"It would be ... a lot harder without people like the trail angels who are willing to drive you around the fires," Teesseling said.
Even if hikers don't encounter active fires, they are confronted with the effects of climate change when walking through fire areas.
Will Georis, 25, hiked the PCT in 2022, the year after the Dixie Fire. The blaze left behind miles of burned stumps, unstable ground and a risk that wind gusts could turn burned trees into widowmakers - the term hikers give to dead trees and branches that threaten to fall.
"You can't get around it - these huge areas where every tree is burned to the ground or it feels like a bomb went off. It's not fun to walk," said Georis, who worked as a wilderness firefighter in college and is now a forest ranger.
"The biodiversity will be different," he added. "There will be different species coming in."
Fire itself is not unnatural or bad. According to researchers at the University of California, Berkeley, before the arrival of Europeans, California burned an average of 4.5 million acres per year - a figure that would surpass modern fire seasons.
But today's forests are not as well adapted to fire and often burn hotter.
"The fires of the past were low intensity," O'Brien said. "That created these really resilient forests where the lower branches of the big trees burned, but their canopy stayed intact, and they survived and kept growing."
Georis has successfully completed a continuous trail from Mexico to Canada, an experience that has become increasingly difficult. He urged future hikers not to be deterred by the potential for confusing logistics, smoke and the need to be flexible with plans - a sentiment shared by many long-distance hikers who say the trail's scenery and community still make it worth the effort.
While many hikers focus on completing a continuous trail, Georis said, "Once you get to the end, you realize that was the least important thing - it really is the people and the experiences."
This article was originally published on NBCNews.com
