Nearly a month after lightning ignited the Big Grass Fire in the high desert near the Oregon-Idaho border, the largest wildfire currently associated with Oregon has reached a markedly different stage of the fight. The fire that raced across hundreds of thousands of acres, threatened homes and ranch country and drew more than 1,200 firefighters at the height of the response is now 85 percent contained, with its enormous perimeter largely holding as crews concentrate on the heat that remains.
The Big Grass Fire stood at 578,639 acres Friday, August 21, according to federal fire officials. Its footprint stretches across Malheur County in southeastern Oregon and Owyhee County in southwestern Idaho, placing nearly 579,000 acres inside a single interstate fire perimeter. Because the incident crosses the state line, that figure represents the entire fire and should not be interpreted as acreage burned exclusively within Oregon.
What has changed most dramatically is no longer the size of Big Grass, but the amount of its perimeter firefighters have brought under control.
For much of early August, acreage and containment were moving in an unwelcome direction. The fire reached more than 513,000 acres by August 9 with less than 40 percent of its perimeter contained. Within days it had surpassed 555,000 acres as firefighters confronted wind-driven runs through dry grass and brush across remote country where access can be difficult and distances between roads are substantial.
By Friday, that rapid expansion had largely stopped. Containment had climbed to 85 percent, the latest acreage calculation included a small mapping adjustment rather than another major increase, and the number of firefighters required on the incident had fallen substantially.
There were 687 personnel assigned to Big Grass Friday, including nine crews, 40 engines and four helicopters. That is 129 fewer personnel than the previous reporting period and roughly half the force assigned during one of the fire’s most demanding periods earlier this month, when more than 1,280 firefighters were working the incident.
The reduction reflects how much of the perimeter has been secured, but it does not signal the end of the fire.
Containment is a measurement of the fire’s perimeter, not a measurement of how much of the interior has stopped burning. At 85 percent containment, firefighters have established control lines around most of Big Grass that they expect will prevent the fire from spreading beyond those sections under anticipated conditions. The remaining portions still require suppression work, while heat can persist well inside portions of the burned landscape long after flames disappear from view.
That interior heat has become one of the central concerns as Big Grass moves deeper into containment.
Around South Mountain and the Owyhee River, firefighters have been working through difficult terrain containing pockets of unburned vegetation surrounded by land already crossed by fire. Those islands can become a problem when heat remains nearby and weather supplies the wind and dry conditions necessary for fire to become active again.
Crews have been searching for those heat sources rather than waiting for visible flames to reveal them. Unmanned aircraft and infrared equipment have helped locate hot spots, helicopters have delivered water into terrain difficult to reach from the ground, and firefighters have opened portions of dozer line to search beneath disturbed soil for buried heat.
The work can be painstaking because a fire approaching containment can appear far quieter than the danger that remains beneath the surface. Roots, heavy vegetation and other material can retain heat for extended periods. If wind reaches those areas while humidity is low, embers can move into vegetation that escaped the original burn or cross a line firefighters previously secured.
Big Grass has already demonstrated that possibility.
Recent thunderstorms produced erratic winds across portions of the fire, while strong gusts and rotating columns of dust and debris disturbed burned ground and carried embers. Firefighters also encountered isolated tree torching around South Mountain. Those conditions required crews to remain positioned along established lines and watch for new ignition outside the principal perimeter.
Weather therefore remains part of the calculation even as the containment percentage rises. Hot temperatures, exceptionally dry air and afternoon winds can test weeks of suppression work in a matter of hours, particularly in the open rangelands of southeastern Oregon and southwestern Idaho.
The evacuation picture has improved considerably, although the emergency has not ended everywhere.
Level 3 “Go Now” evacuation areas remain south of Jordan Valley on the Oregon side of the fire. Across the border, evacuation boundaries in Owyhee County have been reduced as fire conditions improved, and areas including Silver City and Triangle have been removed from evacuation status.
The remaining evacuation notices underscore the difference between a fire that is increasingly controlled and one that is finished. Residents within active evacuation areas must continue following county emergency instructions because those boundaries can be changed as fire behavior, weather and suppression progress are reassessed.
Conditions were considerably more severe earlier in the incident. At one point, officials reported 159 people evacuated, 315 residential structures threatened and hundreds of additional minor structures within areas exposed to the fire. Those numbers describe an earlier period of the emergency rather than the number of people currently displaced, but they illustrate how extensively Big Grass affected the sparsely populated region as its perimeter expanded.
Public access presents a separate issue.
Bureau of Land Management closures remain in portions of the fire area even where immediate evacuation threats have eased. A reduced evacuation level does not automatically reopen public land because the hazards left behind by a wildfire extend beyond active flames.
Burned trees can fall without warning. Fire can weaken root systems and destabilize vegetation. Hot material can remain beneath the surface, and firefighters, engines and heavy equipment may still be operating along roads and across portions of the landscape. Land managers can therefore maintain closures after county officials determine that residents no longer face the same immediate threat.
The scale of the operation is also reflected in its cost. Federal incident reporting placed suppression expenditures at approximately $62.1 million through Friday, covering a response that has required crews, engines, aircraft, heavy equipment, incident management personnel and logistical support across an unusually large and remote fire area.
Big Grass began with lightning on July 23 southwest of Jordan Valley. What followed was not a single uninterrupted advance, but weeks of changing fire behavior across dry grasslands, brush and rugged terrain along the Oregon-Idaho border.
By early August, its acreage was being measured in hundreds of thousands. By August 9, the fire had reached approximately 513,437 acres. It continued beyond 555,000 acres as crews attempted to secure an increasingly long perimeter, and the total eventually approached 579,000 acres.
The numbers began telling a different story during the second half of August.
Instead of acreage continuing to climb by tens of thousands, the footprint began stabilizing. Containment moved above 70 percent, then reached 80 percent and climbed to 85 percent by Friday. At the same time, fire managers began releasing personnel and equipment that were no longer necessary for the level of activity occurring on the incident.
Federal fire officials have listed August 22 as an estimated containment date. That is a planning estimate, not a deadline and not a prediction that every ember across nearly 579,000 acres will be extinguished.
A wildfire can reach full containment while heat remains well inside its perimeter. Crews may continue patrolling, extinguishing hot spots and monitoring burned areas after the containment figure reaches 100 percent. The final stages can continue until fire managers determine that remaining heat no longer presents a realistic threat of escaping control lines.
For Big Grass, that final work is taking place across a landscape transformed since July 23.
The firefighting mission has moved from chasing an expanding perimeter across two states to defending lines already built, locating concealed heat and making certain that unburned pockets inside the fire cannot provide a route for renewed spread. The number of firefighters has fallen, evacuation territory has contracted and the acreage has stopped making the enormous jumps recorded earlier in the incident.
Yet 15 percent of the perimeter remains outside full containment, Level 3 evacuations remain in place south of Jordan Valley, and hundreds of firefighters are still assigned to the incident.
Big Grass is therefore neither the rapidly expanding emergency it was earlier this month nor a wildfire that can yet be considered finished. On Friday, it stands between those two points: 578,639 acres across Oregon and Idaho, 85 percent contained, and increasingly surrounded by the lines firefighters have spent nearly a month building and holding.