The federal wildfire incident feed lists fourteen fires currently carrying an estimated cost to date above $20m. Sorted by cost, the most expensive is Aspen Acres in Custer County, Colorado, at $97.0m. It has burned 101,961 acres and is 68 per cent contained, with 210 people assigned.

The two largest fires in the country are both in Oregon and both cost less. Big Grass has burned 358,911 acres — three and a half times Aspen Acres — for $24.3m. Rowe Creek Complex has burned 340,276 acres for $57.7m. Between them they account for 699,187 acres and $82.0m, which is $15m less than Aspen Acres alone has cost on less than a seventh of the ground.

The comparison is not a story about Oregon being efficient. It is a story about what the cost figure measures. Big Grass works out at $68 an acre and Rowe Creek at $170; Aspen Acres at $951. The number tracks what a fire is being asked to defend, not how much of it there is.

The cleanest test of that is three fires of nearly identical size. Babylon, in San Juan County, Utah, has burned 107,189 acres for $61.3m. Cottonwood, in Beaver County, has burned 97,464 acres for $62.7m. Aspen Acres sits between them on acreage at 101,961 and above both on cost by more than half: $572 an acre, $643 an acre, $951 an acre. All three are within ten per cent of each other in size and all three are now largely or wholly contained.

At the other end of the range the divergence is starker still. The Salmon fire in Oregon has burned 1,426 acres and carries $34.8m — $24,378 an acre, and 405 people assigned to a fire smaller than two square miles. E Evans Creek Rd, also in Oregon, is $4,247 an acre across 15,580 acres with 575 people on it. Willow, in Lake County, Colorado, is $4,989 an acre on 7,196 acres with six people currently assigned. Across the fourteen, the range from $68 to $24,378 an acre is a factor of 360.

Personnel move with cost rather than with size, which is the mechanism. Big Grass has 1,096 people on 358,911 acres. Rowe Creek Complex has 1,678 on 340,276. Cottonwood, at 95 per cent contained, is down to 63 people and Babylon to 86. The expensive fires are the ones still holding crews, engines and aircraft near something worth defending.

One limitation belongs on all of these figures. Estimated cost to date is a running total submitted by each incident through the same ICS-209 reporting system that produces the acreage, so the two numbers share an instrument and a reporting lag, and cost keeps accruing after a fire stops growing. That is why the comparison here is cross-sectional — all fourteen fires pulled in one query, on one afternoon — rather than a reconstruction of how any single fire’s bill accumulated.