Soon after Hernán Cortés arrived in Mexico in 1519, military campaigns and expeditions were initiated to near and distant places, across the Americas and beyond. Whereas the presence of the Spanish Crown in other parts of what is now the US Southwest was established and entrenched (and was challenged by Indigenous groups) during the 1500s and 1600s, the area of what is now southern and central Arizona had historically been more of a place to pass through than to establish a permanent presence until the early 1700s.

The subject of this well-documented book by Deni Seymour and Oscar Rodriguez is a 110-day expedition in 1780, led by military governor Don Jacobo de Ugarte y Loyola and lieutenant of the infantry and engineer of the royal armies Don Gerónimo de la Rocha y Figueroa, across what is now northern Sonora, Mexico, and southern and central Arizona—an area generally known as the Pimería Alta. The 1770s and 1780s was a time of Spanish military and political reorganization of southern and central Arizona, including moving and reducing the numbers of presidios (military forts) in the area and further inventorying through expeditions the lands that had been claimed for the Spanish Crown. As a result, the expedition by Ugarte and Rocha was designed in part to better understand this area and identify possible locations for moving presidios or establishing new ones. The culmination of the expedition was a 1780 map (“Mapa de la Frontera de Sonora para el Establecimiento de la Linea de Presidios,” translated as “Map of the frontier of Sonora for the establishment of the line of presidios”) described by many scholars as the most detailed map of southern Arizona and northern Sonora ever produced during the Spanish period, indicating approximate locations of many Indigenous communities and Spanish settlements and details about them.

The map and accompanying journal from the expedition are the focus of this book. After an introductory chapter, Chapter 2 documents justifications for the expedition and specific instructions given to Ugarte and Rocha by Commandant-General Teodoro de Croix for their expedition and reconnaissance. The ultimate goal of the expedition was to fulfill royal instructions from 1772 to realign the presidios in the region. Chapter 2 offers great detail on portions of the instructions, including treatment of Native peoples they encounter, as well as consideration of presidios in the region to be examined and documented by Ugarte and Rocha. Chapter 3 offers intriguing summaries of field reports by the expedition back to Commandant-General de Croix. Chapter 2 highlights elements of Ugarte and Rocha's detailed map, illustrating the presidios and other locations mentioned in the text; the map detail is incredible. Chapter 3, in contrast, includes more contemporary maps, photos, and figures relevant to the text.

Chapters 4 and 5 offer more detailed information on the expedition itself. Chapter 4 documents the expedition route, including maps offering precise locations of daily progress. The detail in this chapter provides information that is generally lacking from studies of other expeditions in the greater region of which I am aware. The map itself is uniquely detailed in and of itself. It offers keen insights into the regional landscape, and it marks the locations of proposed new presidios. Chapter 4 discusses details on the map and its connections to the corresponding expedition diary, and differences between the map and diary. Chapter 5 presents the translated text of Rocha's diary. Like the preceding chapter, Chapter 5 connects details in the diary to the map and notes discrepancies between them. This chapter also offers much more detailed blowups of portions of the map corresponding to specific information drawn from the diary. In addition to maps, there are also several modern photographs orienting readers to the present-day area.

The last four chapters of the book (Chapters 6–9) further analyze these cartographic and documentary data. What can we learn from the map, diary, and summary reports about Indigenous peoples and colonial groups as well as the larger landscape of the 1780s? How does such knowledge connect with the present? Chapter 6 considers regional environmental history through the lens of the expedition and outlines a baseline for considering and assessing historical change. The authors focus here in part on important topics such as arroyo cutting, historical water flows, and environmental degradation more generally. Chapter 7 focuses on elements of the expedition's map and diary to consider what the authors argue is one of the most important insights from these documents: the practices and customs of local Indigenous peoples. Discussion here focuses on the O'odham, including the Sobaipuri O'odham, who the authors argue have been ignored or overlooked by many historians. Chapter 8 focuses on the Apache. The authors note that the map and corresponding expedition diary are as intriguing for which Native groups they mentioned as for those they did not. This chapter offers context to the insights given by Rocha's diary regarding the Apache and other groups, Spanish perceptions of them, and how the Spanish may wish to locate or relocate presidios in response to raids by Indigenous groups. Chapter 9 offers concluding remarks and high-level assessment of the implications of the expedition diary and map for understanding Spanish perceptions of the region's physical terrain and Spanish strategies to adjust their settlements accordingly. It also addresses what we can learn about Indigenous peoples of the region from these documents.

Overall, I am impressed with the treatment in this book of an historic expedition seldom seen in such detail. Seymour and Rodriguez provide keen insight into the larger context of what scholars can learn from these documentary sources about Indigenous peoples and environments. Seymour especially has worked in this region for decades, and she brings longitudinal insight to bear on the analysis of the expedition map and diary. Although To the Corner of the Province will be of interest to historians and archaeologists in southern Arizona and northern Sonora, its analytical chapters will also be of interest to a wider range of scholars, including those studying environmental history.