Paper Trails presents a new history of the American state and its efforts to conquer, occupy, and integrate the western United States between the 1860s and early 1900s. The success of this project depended on an unassuming government institution: the US Post. As millions of settlers rushed into remote corners of the region, they relied on the mail to stay connected to the wider world. Letters and newspapers, magazines and pamphlets, petitions and money orders, all traveled across the most expansive communications network on earth. Paper Trails maps the year-by-year spread of this infrastructure using a dataset of more than one hundred thousand post offices, revealing a new and unfamiliar picture of the federal government in the West. Despite its size, the US Post was both nimble and ephemeral, rapidly spinning out its infrastructure to distant places before melting away at a moment’s notice. The administration of this network bore little resemblance to the civil service bureaucracies typically associated with government institutions today. Instead, the US Post grafted public mail service onto the private operations of thousands of local businesses, contracting with stagecoach companies to carry bags of mail and paying local merchants to distribute letters from their stores. The postal network’s sprawling geography and localized operations force a reconsideration of the American state, its history, and the ways in which it exercised power. This book tells the story of one of the most dramatic reorganizations of people, land, and resources in American history and the underlying spatial circuitry that wove this project together.