In April 1780, Military Governor Ugarte and Chief Engineer Rocha were sent on a reconnaissance mission through the northwestern frontier of New Spain, land that today is northern Sonora and southeastern Arizona. Seeking information on the advisability of placing a presidio at the junction of the San Pedro and Gila rivers, Ugarte and Rocha described the landscape in unprecedented detail. Their accounts provide valuable baseline information on environment and culture that allows for analysis of changes at a critical moment in borderland history. To the Corner of the Province provides not just the translations of their orders, summary reports, journal, and map, but commentary informed by a variety of sources. Drawing on ethnography, borderland history, ethnohistory, oral history, and archaeology, authors Seymour and Rodriguez elucidate the significance of these documents, expounding on the content and providing a glimpse into the harsh realities and intrinsic beauty of the region. Seymour’s more than thirty years’ experience working in this part of the Southwest adds depth and perspective to the narrative.