In this article we examine the curious stability of outdoor penal labour in California in the 20th century against a shifting social and penal field. Analysing state archival data on prison highway and forestry camps between 1915 and 2000, we frame the persistence of these practices as evidence of a penal labour palimpsest. We demonstrate how the agency and interpretive innovation of penal administrators – as the architects and interpreters of this palimpsest – served as a stabilising mechanism akin to, but distinct from, existing theories of path dependence. Zooming out from the intricacies of the historical record, we position this case as revealing some of the limits of strict theories of path dependence and, instead, as offering a more dynamic understanding of the complex, intersecting and malleable ways in which history matters.