The Sediments of History: Placing Arizona in the Columbian Exchange

Arizona's environmental history has been one of dispersion, collecting, and redepositing, of erosion and formation, both human and geological. Biological change induced by the fifteenth- and sixteenth-century Columbian Exchange of diseases, horses, sheep, and wheat between Europe and the Americas created new and layered erosion and flood patterns to which humans responded by movement. Arizona's landscape amplified erosive impacts because, as environmental historian Diana Davis notes, "a majority of the arid and semiarid zone has ecological dynamics that are not at equilibrium due to the scarcity of rainfall and the high variability of its occurrence."¹

This essay explores how layers of erosion and sedimentation unleashed during the early modern Columbian Exchange accelerated in the eighteenth and nineteenth centuries, creating the conditions of structured inequality maintained by federal policy in Arizona during the twentieth century.² Building on Cynthia

A farm near Springerville after irrigation from the Little Colorado River. Photograph by Russel Lee. Courtesy of Library of Congress. https://www.loc.gov/item/2017785997/

Radding's use of social ecology as "a living and changing complex of relations that developed historically among diverse human populations and with the land they occupied," this essay suggests that extending Radding's narrative of "wandering peoples" to Arizona in the nineteenth century reveals increased erosion, then imposed sedimentation.³

Following virgin soil epidemics in the sixteenth century, the Columbian Exchange in Arizona burned slow in the early modern era, largely uncontrolled by imperial states. Then it erupted in the eighteenth and nineteenth century with multiple layers of erosion and sedimentation, connecting regional histories in the Colorado Plateau, the lower Colorado River, and the Gila River watershed. Before the 1860s, ecologies of disease, livestock herds, and entangled imperial alliances produced new patterns of migration, trade, and resource allocation. After the 1860s, these movements collected on the abutments of Anglo-American capitalism, the way silt collects behind a dam or sagebrush behind fences. Forts, mines, wagon roads, and irrigation canals accelerated this process. By the twentieth century, seasonal floods flowed faster and cut deeper, subjecting humans to multiple erosive forces. Livestock herds crossed gullies and newly cut arroyos. Eventually, the U.S. federal government took a larger role in the region to manage the layers of sedimentation and erosion unleashed by this human activity. Much like sediment on a river bottom, these developments overlaid each other as new erosive flows entered the region.

The Columbian Exchange and Environmental History

Environmental historians, including Alfred Crosby, Donald Worster, and Richard White, who emphasize the primacy of aridity on the region, trace the environmental changes that followed the arrival of Europeans.⁴ Three bodies of environmental history scholarship inform this essay: (1) the Columbian Exchange and ecological imperialism to explain the erosive force of new biota; while (2) borderlands environmental history; and (3) large technological systems studies both emphasize how erosion was stabilized and channelized in the late nineteenth and early twentieth centuries. Together, this scholarship suggests that the Columbian Exchange was not only a force of early modern imperialism but also of nineteenth-century capitalism and twentieth-century state-sponsored modernization projects.

Alfred Crosby's The Columbian Exchange emphasizes how European and American plants and animals mixed in the centuries after contact. His Ecological Imperialism considers how this mixing assisted conquest and colonization through the transport of European "portmanteau biota," the collapse of native ecology, and the creation of "Neo-Europes" in temperate regions with weather patterns most favorable to Old World plants and animals.⁵ Both works view this exchange as primarily unfolding in temperate regions: "there are wide stretches of the Americas where European flora and fauna did not and do not prosper," Crosby writes, especially those in the "hottest, coldest, driest, wettest, and, in general, the most inhospitable" regions.⁶

Within this framework, environmental historians have struggled to fit Arizona into the Columbian Exchange, despite waves of transplanted European disease, livestock, and crops that shaped its history. Many conclude, as does Crosby, that Arizona's desert environment functioned as a barrier...