We tested for changes in forest structural classes from 1860 to 1940 in 26 dry Pinus ponderosa–Pseudotsuga menziesii stands of northeastern Washington. In 1860 historical fire regimes and associated forest structure remained mostly intact; aerial photos of national forest lands in eastern Washington were taken 70–80 years later and used as historic reference points in regional resource assessments. We determined changes in stand age, tree density, and number of age cohorts per stand between 1860 and 1940. Also, we evaluated whether stand age-class structure in 1860 was in agreement with fire-scar analysis estimates of the historical fire regime. We developed a forest structure classification based on age cohorts and found that forest structural classes varied significantly (P < 0.001) from 1860 to 1940. From 1860 to 1940, average stand age increased by 26% and number of age cohorts per stand increased by 18%. Stands in stand initiation structural classes declined from 27% to 4%; stands in old forest structural classes increased from 23% to 49%. We suggest the 1940 photo record, previously used to assess historical conditions, may provide a false metric of structural complexity for historical dry fir-pine forests in eastern Washington. Competing interpretations of stand age-class structure in 1860 prevented the conclusive verification of historical fire regimes.