Firefighters were working in extreme temperatures across the U.S. West and struggling to contain wildfires, the largest burning in California and Oregon, as another heat wave baked the region, straining power grids.

The largest wildfire of the year in California — the Beckwourth Complex — was raging along the Nevada state line and has burned about 140 square miles (362 square kilometers) as of Monday morning and state regulators asked consumers to voluntarily “conserve as much electricity as possible” to avoid any outages starting in the afternoon.

In Oregon, the Bootleg Fire exploded to 240 square miles (621 square kilometers) as it raced through heavy timber in the Fremont-Winema National Forest, near the Klamath County town of Sprague River. The fire disrupted service on three transmission lines providing up to 5,500 megawatts of electricity to neighboring California.

A wildfire in southeast Washington grew to almost 60 square miles (155 square kilometers) while in Idaho, Gov. Brad Little has mobilized the National Guard to help fight fires sparked after lightning storms swept across the drought-stricken region.

The blazes come as the West is in the midst of a second extreme heat wave within just a few weeks and as the entire region is suffering from one of the worst droughts in recent history. Extreme heat warnings in California were finally expected to expire Monday night.

READ: California witnesses 7,860 wildfires, 3.4 mln acres burned this year

On Sunday, firefighters working in temperatures that topped 100 degrees Fahrenheit (38 Celsius) were able to gain some ground on the Beckwourth Complex, increasing containment to 23%.

Late Saturday, flames jumped U.S. 395, which was closed near the small town of Doyle in California’s Lassen County. The lanes reopened Sunday, and officials urged motorists to use caution and keep moving along the key north-south route where flames were 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.”

Cagle said structures had burned in Doyle, but he didn’t have an exact number. Bob Prary, who manages the Buck-Inn Bar in the town of about 600 people, said he saw at least six houses destroyed after Saturday’s flareup. The fire was smoldering Sunday in and around Doyle, but he feared some remote ranch properties were still in danger.

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“It seems like the worst is over in town, but back on the mountainside the fire’s still going strong,” Prary said.

A new fire broke out Sunday afternoon in the Sierra Nevada south of Yosemite National Park and by evening covered more than 6 square miles (15.5 square kilometers), triggering evacuations in areas of two counties. Containment was just 5% but the highway leading to the southern entrance of the park remained open early Monday.

In Arizona, a small plane crashed 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 northwest of Phoenix.

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Officials on Sunday 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 U.S. Forest Service. The National Transportation Safety Board is investigating the crash.