The Bitterroot Valley in western Montana was the primary American site of Diamond's contemporary fieldwork for Collapse. Beginning in the 1990s, Diamond conducted interviews with residents and documented the environmental transformation the valley had undergone — forests reduced, rivers degraded, summers increasingly filled with smoke from wildfires — and the residents' own perceptions of that change. The striking finding was that older residents could describe the transformed landscape but could not identify when the transformation had occurred. Each year's conditions had been only marginally different from the previous year's; the cumulative change was enormous; the incremental experience was unremarkable. The case became Diamond's empirical grounding for the concept of creeping normalcy.
The Bitterroot Valley is located in western Montana, historically one of the most productive and biologically diverse valleys in the northern Rockies. Native American inhabitation dates back millennia; European settlement intensified in the late nineteenth century with timber, cattle, and mining industries. The valley's environmental trajectory over the twentieth century included significant deforestation, riparian degradation from ranching and irrigation, fire suppression that produced progressively more catastrophic wildfires, and demographic changes that brought new populations into a landscape they had not experienced in its earlier state.
Diamond's method was ethnographic. He interviewed long-term residents — families that had been in the valley for multiple generations — and asked them to describe environmental changes they had observed. The interviews revealed a specific pattern: residents could articulate, clearly and in detail, that the valley was substantially different from their childhood memories. Forests they remembered were gone. Rivers ran murkier. Summer smoke from wildfires, once rare, had become annual and increasingly prolonged. Animal populations had shifted. Specific species had become scarce or absent.
But when asked when these changes had occurred, the residents could not identify specific years or even specific decades. The change had been slow enough that no year's conditions had seemed dramatically different from the previous year's. Each year's new normal had been only marginally different from the last. The cumulative effect, across the residents' lifetimes, was striking; the incremental experience, across any single year, had been unremarkable.
The case gave Diamond the empirical grounding for the creeping normalcy concept that would become central to Collapse. The Bitterroot residents were not unusually unperceptive; they were exhibiting a universal feature of human perception. The baseline against which change is measured shifts continuously with current conditions, and the cumulative shift can be enormous without any single moment of shift being dramatic enough to register. The concept would then be applied retroactively to Diamond's collapsed-civilization cases, where the same dynamic — invisible cumulative change — appeared with structural regularity.
Diamond's Bitterroot Valley fieldwork was conducted primarily in the 1990s and early 2000s, forming one of the contemporary American case studies in Collapse (2005). The valley provided Diamond with the empirical grounding for creeping normalcy that complemented his historical and archaeological cases — a contemporary demonstration that the cognitive mechanism he was analyzing operated in the present, not only in the deep past.
The methodology drew on oral history and environmental perception research (notably the shifting-baseline work of Daniel Pauly in fisheries science), which had independently documented the same phenomenon of generational perception drift in environmental resources.
Residents could describe cumulative change but not date it. The disconnect between clear perception of total change and inability to identify when it occurred is the empirical signature of creeping normalcy.
The baseline shifts continuously. Each year's conditions become the reference point for the next year's comparison, producing systematic underestimation of cumulative change.
The pattern operates regardless of education or attentiveness. The Bitterroot residents were generally knowledgeable about their environment; the perceptual limitation was structural rather than a failure of attention.
Generational transition compounds the effect. Newer residents had no experiential baseline for earlier conditions; older residents' memory of those conditions was isolated rather than collective.
The case generalizes. Similar patterns documented in marine fisheries, forest ecosystems, and other resource systems suggest that creeping normalcy is a robust feature of environmental perception rather than a Bitterroot-specific phenomenon.
Some critics have argued that Diamond's Bitterroot analysis was ethnographically thin — that the interviews were not systematic enough to support the sweeping generalization about creeping normalcy. Defenders respond that the ethnographic data was corroborated by extensive environmental historical research on the valley (timber records, fire history, species distributions) which documented the cumulative change independent of residents' perception, and that the empirical pattern aligned with similar research in other contexts. The case remains a standard teaching example of creeping normalcy, both in environmental humanities and in contemporary work on AI-era cognitive drift.