In Twilight of the Mission Frontier, José Refugio De la Torre Curiel provides a comprehensive analysis of the ways in which Franciscan mission communities in Sonora changed within the context of the late eighteenth and early nineteenth centuries. The work is bounded by the start of Franciscan administration of missions in Pimería Baja, Opatería and Pimería Alta, along with the last Franciscan's departure in 1855, with a strong focus on the late colonial period. De la Torre understands Sonoran missions as dynamic spaces of multiple meanings for different actors, whose social functions changed due to factors such as the extent of non-Indian settlement, the degree of acceptance of the friars’ regimes, and the mission economies’ interactions with local and regional markets.

Instead of trying to understand the forces which led to the ‘failure’ of the mission regime in Sonora, De la Torre explores the internal components of mission complexes, the functions they served within Sonoran communities and the ways in which they interacted with other settlers. During this period friars from the apostolic college of Querétaro focused their efforts on the northern and westernmost missions, while Xaliscan friars administered those in the more developed eastern and southern areas. The boundaries of mission districts were fluid, and administrative and economic structures also changed depending on the politics and demographics of each area. Where earlier missions, and those in other regions such as Alta California, provided social organisation, linked native peoples to material culture and mediated intercultural contact, those roles eroded and changed in late colonial Sonora, so that by the early national period missions and their friars were no longer central actors in the interactions among groups within the region.

Twilight of the Mission Frontier is organised chronologically and thematically. First, the author provides an overview of Sonora's history, presented as a commentary on civil and religious officials’ descriptions of the province in three different periods: before 1740, between 1740 and 1767, and after 1768. This analysis of differing narratives about the Sonoran landscape demonstrates the ways in which varied perceptions of this frontier space reflected the constant flux of relations between people and their environments. The next four chapters consider the demographic, cultural, economic and administrative changes in the mission districts of Sonora. De la Torre draws upon mission census lists to define the zones and moments in which demographic changes affecting the Indian population took place, contrasting the multi-ethnic and growing Spanish character of the Pimería Baja-Opatería districts with the largely indigenous settlements in Pimería Alta. Maps, tables and graphs within the second chapter provide visual representations of the demographic changes. A large chapter on transculturation and pluri-ethnic mobility explores the evolving and symbiotic relations between mission residents and other individuals and groups. As the social function of the missions changed, their residents took more responsibility for their own religious and economic activities, eventually aligning themselves with local elites instead of the missionaries. The discussion of changes in religious practices, material culture, diet, mobility and cultural mediators would benefit from a more careful analysis of women and changing gender roles. De la Torre finds that pluri-ethnic mobility within and among groups, towns and missions for work and marriage helped Sonorans manage competing labour, state and religious demands. When missions ceased to fulfil useful social functions, their residents simply withdrew from mission life.

In chapter 4, an examination of the Sonoran economy in the late colonial and early national periods reveals a captive network characterised by large profit margins for merchants, maintained at local levels through mechanisms such as paying wages in kind, credit sales, advances of goods, and setting the same prices for different qualities of goods such as Brittany cloth. The scarcity of currency, high prices of goods and captivity of consumers hurt Indians and poor vecinos most, and De la Torre compares the situation with debt peonage during the Porfiriato. From an examination of the economy, the work turns to the nuances of differing systems of mission administration. Three distinct generations of Franciscans had differing goals and obstacles in organising mission life. In addition, the Xaliscan and Queréteran friars worked with distinct populations, which resulted in different modes of administration. Disputes among secular and regular clergy and political officials ultimately led to more freedom for Indians, who left the mission more frequently and developed stronger relationships with intermediaries other than the friars. The final pages of the book trace the material and economic decline of the missions, examining contributing factors such as labour demand and payment, the changing status of Indians through the independence and early national periods, the expulsion of Spanish friars and the secularisation of the missions.

The book is well grounded within literature on colonial and early national Latin America, as well as works on borderlands missions. De la Torre draws upon demographic, cultural and institutional variables to compare Querétaran and Xaliscan mission districts. He utilises mission census lists, reports and letters written by political and ecclesiastical visitors and the friars, as well as account books from merchants and mission records, to craft his arguments. This large body of source material allows for nuanced analyses of changes in the economics, politics, culture and administration of groups associated with the mission complexes, although the economic and administrative sections of the study are strongest. Twilight of the Mission Frontier is an important regional study for its synthesis of a wide variety of primary and secondary sources. It will be of interest to students and scholars of Sonora and the northern Spanish borderlands, as well as those who study mission complexes in other places and time periods.