US firefighters working in searing heat have struggled to contain the largest wildfire in California this year.
Meanwhile, state power operators urged people to conserve energy after a huge wildfire in neighbouring Oregon disrupted the flow of electricity from three major transmission lines.
A large part of the US west baked during the weekend in triple-digit temperatures which are expected to continue into the start of this week.
The California Independent System Operator which manages the state’s power grid issued a five-hour “flex alert” starting at 4pm on Monday (midnight BST) and asked consumers to “conserve as much electricity as possible” to avoid any outages.
California and other parts of the US west are sinking deeper into drought which has sent the risk of fire sky-high in many areas.
In Arizona, a small plane crashed on Saturday during a survey of a wildfire in rural Mohave County, killing both crew members.
The Beech C-90 aircraft was helping perform reconnaissance over the lightning-caused Cedar Basin Fire, near the tiny community of Wikieup, north-west of Phoenix.
Officials identified the victims as Air Tactical Group Supervisor Jeff Piechura, 62, a retired Tucson-area fire chief who was working for the Coronado National Forest, and Matthew Miller, 48, a pilot with Falcon Executive Aviation contracted by the US Forest Service.
The National Transportation Safety Board is investigating the crash.
In Oregon, the Bootleg Fire spread to 224 square miles as it raced through heavy timber in the Fremont-Winema National Forest, near the Klamath County town of Sprague River.
The blaze disrupted service on three transmission lines providing up to 5,500 megawatts of electricity to neighbouring California.
The largest wildfire of the year in California was raging near the border with Nevada.
The Beckwourth Complex Fire – a combination of two lightning-caused blazes burning north of Lake Tahoe – grew by a third on Sunday to 134 square miles.
However, firefighters working in temperatures that topped 100 degrees Fahrenheit (38C) were able to gain some ground, doubling containment to 20%.
Late on Saturday, flames reached the US 395 road, which was closed near the small town of Doyle in California’s Lassen County. The lanes reopened on Sunday, and officials urged motorists to use caution and keep moving along the key north-south route where flames are still active.
“Do not stop and take pictures,” said the fire’s operations section chief Jake Cagle. “You are going to impede our operations if you stop and look at what’s going on.”
Meanwhile, a wildfire in southeast Washington grew to almost 60 square miles as it blackened grass and timber while it moved into the Umatilla National Forest.
In Idaho, governor Brad Little declared a wildfire emergency on Friday and mobilised the state’s National Guard to help fight fires sparked after lightning storms swept across the drought-stricken region.
