A fast-growing wildfire blazing across southwest Oregon has burned through more than 153,500 acres, forced hundreds of evacuations and is imperiling a major power grid as much of the West endures yet another heat wave.

The Bootleg Fire, the biggest of nearly 60 large fires burning mostly in Western states, has been spreading uncontrolled for six days, doubling in size three times over the weekend. It threatened electric transmission lines that supply energy to California, leading the state to make emergency calls for power conservation.

Coming so early in the season, the Bootleg Fire’s size and intensity has officials worried about the months ahead. More than 1,000 firefighters were on the scene Monday, with more expected to join the effort.

“The fire behavior we are seeing on the Bootleg Fire is among the most extreme you can find and firefighters are seeing conditions they have never seen before,” Al Lawson, an incident commander for the fire, said in a statement.

Across parts of Klamath County, near the California border in southern Oregon, authorities ordered evacuations, urging residents to “go now.” The Klamath County Sheriff’s Office began issuing citations and said it would make arrests to keep people out of those areas, a rare step to enforce evacuation compliance as some residents have not heeded warnings.

By early Monday evening, flames had destroyed at least 50 structures, including seven homes, Gert Zoutendijk, a fire marshal assisting the response, told The Washington Post. In all, nearly 2,000 structures are at risk, authorities said.

The California Independent System Operator (CISO), which manages electricity for a power grid that serves 80 percent of California, called the fire “a wild card” and said it has made transmission lines from Oregon “unreliable.” As of Monday evening, efforts by customers to conserve power had worked, keeping the grid stable, the CISO tweeted.

The blaze is threatening the California Oregon Intertie, also referred to as Path 66, a key link that shuttles power between the Northwest and California. The fire “tripped off transmission lines” Friday and Saturday, the CISO said, “limiting electricity flow.”

The lines can normally transport 4,400 megawatts, but are now down to just 428, said Maryam Habibi, a spokesperson for the Bonneville Power Administration, a federal agency that operates the intertie. The dense smoke hanging over the area is main barrier to restoring service, Habibi said.

The CISO issued a “flex alert” for Monday night, urging customers to conserve energy to help stabilize the power grid in anticipation of high electricity demand.

The threat to a major power conduit, one expert said, underlines the need to better prepare for the effects of the changing climate on energy infrastructure.

“We’re seeing climate change impacts are here — period,” said Alexandra von Meier, director of electric grid research at the University of California at Berkeley’s Institute for Energy and Environment. “It would behoove us to think about how we can manage, not if, but when we have major failures of the electric grid, which could happen for climate- and weather-related reasons or other reasons.”

The fire started Tuesday afternoon in Fremont-Winema National Forest, about 15 miles northwest of Beatty, and it persisted under hot, dry and windy weather in the area, officials said. The cause is under investigation.

The weather, as well as “extremely dry fuels” from a persistent drought, contributed to “extreme” fire behavior, officials said in an update Sunday.

Conditions had escalated Saturday, prompting firefighters to stop working and retreat to predetermined safety zones, officials said. The fire has been out-of-control since Friday.

Emergency officials said eight large and uncontained wildfires had burned through more than 220,000 total acres in Oregon and Washington, including the Bootleg Fire.

About 250 miles south, in California’s Plumas National Forest, two fires formed the Beckwourth Complex and tore through nearly 90,000 acres, engulfing buildings and cars in flames. It was 23 percent contained as of Monday evening.

And across the West, dozens of active fires burned more than 860,000 acres, an area nearly three times the size of Los Angeles, according to the National Interagency Fire Center.

The coinciding wildfires generated smoke that spread over “most of the western half of the U.S.," the National Oceanic and Atmospheric Administration said.

As the fires burned, more than 30 million people were under excessive heat warnings and advisories, and the National Weather Service forecast the heat wave to linger in much of the West through Tuesday, highs in the upper 90s to 100 degrees in the interior Pacific Northwest.

The latest heat wave comes after the Pacific Northwest endured a deadly “heat dome” late last month. The death toll from that event in Oregon alone has reached 116.

The fatal event was “virtually impossible” without climate change, scientists found.

Read more: