Oregon’s Big Grass Fire has burned 578,000 acres, the largest US wildfire on the books this year

A grass fire that started on rangeland in eastern Oregon in late July has grown into the largest wildfire recorded anywhere in the United States this year. The Big Grass Fire, burning across Malheur County near the Idaho border, has charred 578,637 acres and stands at 94 percent containment, according to federal wildfire tracking data, a footprint larger than the state of Rhode Island.

The Largest Wildfire on the Books This Year

No other wildfire in the country has surpassed the Big Grass Fire’s footprint in 2026, a distinction that reflects both the scale of the blaze and the remote, sparsely populated terrain where it has burned. Malheur County sits in Oregon’s high desert, a landscape of open rangeland and sagebrush steppe far from the state’s population centers, which helps explain why a fire of this size drew relatively little national attention even as it grew past half a million acres.

The fire is one of several major blazes to hit Oregon this season, but its size sets it apart. At 578,637 acres, it covers an area larger than Delaware, a comparison that captures the scale better than the acreage figure alone. Federal incident trackers list the fire under the designation “ORVAD Big Grass Fire,” reflecting its origin within the jurisdiction of Oregon’s Vale District, which manages a large stretch of public rangeland across Malheur County.

Weeks of Growth Since a Natural Start

Fire records list the Big Grass Fire’s discovery date as July 23, 2026, with a natural cause, consistent with a lightning-sparked ignition typical of dry rangeland fires in the region. From that starting point, the fire expanded rapidly through the summer, driven by dry grass fuels that carry flame quickly across open ground once conditions align. Lightning-caused rangeland fires are common in eastern Oregon during the peak of summer, when thunderstorms frequently produce more dry lightning strikes than rainfall, igniting fuels that have already cured under weeks of heat.

Grass and rangeland fires behave differently from forest fires. Fine, dry fuels like cured grass can ignite and spread far faster than timber, allowing a fire to cover tens of thousands of acres in a single wind-driven day even though the flames themselves may burn less intensely per acre than a forest crown fire. That dynamic is a major reason the Big Grass Fire was able to reach its current size in a matter of weeks rather than the months it often takes a forest fire of comparable acreage to develop.

Nearing Full Containment

Suppression crews have brought the fire to 94 percent containment as of the most recent update, according to federal incident tracking. Containment measures the percentage of a fire’s perimeter that crews have secured with fire lines, not the percentage of the burned area that has stopped smoldering, so a high containment figure indicates the fire is largely under control even while some interior areas continue to burn out on their own.

The fire’s size has not changed in the most recent reporting period, a sign that growth has effectively stopped even as containment work continues along the remaining open sections of the perimeter, according to fire-tracking data compiled from the same federal incident feeds. Roughly 226 personnel remained assigned to the incident in the most recent update, a crew size that has scaled down considerably from the fire’s peak staffing as containment lines have held.

A Season Stacked With Oregon Megafires

The Big Grass Fire was not an isolated event this season. Oregon recorded several other fires exceeding 200,000 acres in 2026, including the Rowe Creek Complex at 373,927 acres, the Crosswhite Fire at 342,923 acres, the Coleman Creek Fire at 308,863 acres, and the Hay Creek Complex at 200,292 acres. Combined, those five fires alone burned an area larger than the state of Delaware several times over, marking one of the more severe wildfire seasons the state has recorded in recent years.

Most of those fires, like the Big Grass Fire, burned in Oregon’s less populated eastern and southeastern regions, which meant the scale of the season’s damage did not generate the same level of coverage as fires closer to major West Coast population centers, even though the combined acreage rivaled or exceeded some of the state’s more widely reported fire years. Ranchers and rural communities across Malheur County bore the brunt of the impact, with grazing land and rangeland infrastructure among the most affected assets rather than homes or commercial buildings.

Why Grassland Fires Grow So Fast

Rangeland fires like the Big Grass Fire tend to move quickly because of how little moisture their fuels hold by late summer. Grasses that green up in spring dry out completely within weeks once temperatures rise, turning entire hillsides into continuous, fast-burning fuel beds. Combined with the open terrain of the high desert, which offers few natural barriers like rivers, rock outcrops or major roads to slow a fire’s spread, that dryness allows a rangeland fire to expand across tens of thousands of acres in conditions that would take a forest fire far longer to cover. The Big Grass Fire’s trajectory, from ignition in late July to nearly 579,000 acres and 94 percent containment by early September, reflects that pattern closely, and fire managers in the region increasingly treat grassland fuel conditions as a leading indicator of how severe a given summer’s fire season is likely to become.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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