Firefighters in central Oregon made progress in their battle against ablazethat triggered evacuations and astate of emergencyas it tore across swaths of rugged land, destroying four homes and threatening hundreds of other buildings. The Cram Fire, which has become the nation's largest wildfire this year, has charred 150 square miles of land, an area larger than the size of Las Vegas. The blaze broke out on July 13 and burned for several days before undergoing explosive growth fueled by strong winds, high temperatures and low humidity. It was at 49% containment as of Sunday, July 20. The fire ignited near Willowdale, a sparsely populated area about 133 miles southeast of Portland, and swept through grasslands and rangeland in the region, fire officials said. The cause of the blaze is unclear and remains under investigation, officials said. If the Cram Fire grows by more than 4,200 acres, it will reach what's known as megafire status, meaning it will have burned more than 100,000 acres of land. Evacuation orders and warnings remain in place across at least three counties, including Jefferson, Wasco and Crook County, according toCentral Oregon Fire Information. In a statement on July 20, fire officials said they anticipate cooler weather, possible rain and higher humidity to "moderate fire behavior." Firefighters in Oregon have been aided by increasingly cooler and humid weather, which is expected to continue for the next few days. More than 930 fire personnel responded to the blaze and worked to stop its rapid spread. On July 20, crews traversed rugged terrain as they used dozers to carve containment lines. They recently focused on the southern edge of the blaze, thinning juniper trees along the fire lines to reduce potential fuels. Some personnel who were brought in to protect homes, businesses and other structures will be released as containment grows and cooler weather lingers, according to theCentral Oregon Fire Information. "Remaining personnel will continue working around structures to extinguish hot spots and ensure any lingering threats to homes are addressed," the fire agency said. While the Cram Fire was the largest wildfire in the nation, it was far from the only blaze scorching wide swaths of land. In northern Arizona, a pair of wildfires burningat or near the Grand Canyon North Rimhave charred over 70,000 acres of wildland.The White Fire, which devastated a section of the park, consuming a historic cabin and dozens of other buildings, was at 12,645 acres and 8% containment as of July 20. In western Colorado, crews working a series of wildfires made gains over the weekend, setting up fire lines and increasing containment percentages. The largest of the wildfires, the Deer Creek Fire, has consumed 16,340 acres of land in Colorado and Utah and was at 22% containment. The National Weather Service issued red flag warnings in Nevada and Wyoming as meteorologists anticipate "critical fire weather" on Monday, July 21. The weather warnings urge residents to avoid activities that could spark a fire, including yard work, target shooting, discarding cigarettes outdoors and lighting campfires. "A Red Flag Warning means that critical fire weather conditions are either occurring now, or will shortly," read a warning from the weather service office in Elko, Nevada. "A combination of strong winds, low relative humidity values, and warm temperatures can contribute to extreme fire behavior." This article originally appeared on USA TODAY:Cram Fire in Oregon rages as it nears megafire status