A wildfire burning in southern Yosemite National Park has scorched more than 4,200 acres, and investigators believe hikers may hold the key to what started it. The Dome Fire ignited on September 15 near the Chilnualna Falls Trail, close to the park's South Entrance and the famous sequoias of Mariposa Grove. As of September 25, CalFire lists it at just 17 percent contained.

Park rangers are specifically interested in the week before the fire began. Anyone who walked the trail between September 9 and 15 and saw people with a campfire is being asked to contact the National Park Service at 888-653-0009, submit a tip online, or email nps_isb@nps.gov. Campfires were banned along the entire trail from August 7 because of hot, dry, windy conditions, so any fire spotted there would be significant. Investigators can often pinpoint a fire's origin from burn patterns and physical evidence once flames are knocked down, but eyewitness accounts can speed that up considerably.

The fire has already cost lives. On September 20, firefighting pilots Greg King and Ryan Cutter died when their Super Puma helicopter, working with a water bucket near Ostrander Lake, crashed. The FAA is investigating.

For travellers, the practical picture is mixed. Glacier Point Road was temporarily closed on September 23 due to poor visibility from smoke, cutting off access to several trailheads. But Mariposa Grove, Yosemite Valley and Tuolumne Meadows all remain open, and the Yosemite Mariposa County Tourism Bureau says guided trips are largely operating normally, with some itinerary reshuffling. The advice from local tourism officials goes beyond campfires too: something as mundane as dragging tow chains can throw sparks, so check your vehicle and trailer before driving into fire country.

This isn't a one-off problem. Yosemite's own fire-prevention guidance notes that campfires, cigarettes and general carelessness spark unwanted fires every year. Back in 2006, an uncontrolled campfire ignited the Boundary Fire, which burned over 500 acres and led officials to close popular El Capitan-area trails at the height of the season.

If you've got a Yosemite trip booked this autumn, keep an eye on park alerts, build some flexibility into your route, and assume fire restrictions are in force. And if you happened to be on the Chilnualna Falls Trail that second week of September, the park would like a word.

Story via Outside Online