This dissertation is the story of the meeting of a frontier Mexican legal culture with American colonization and occupation and of the hybrid legal culture that resulted. It focuses in particular on the area now known as El Paso County, Texas, which before 1848 was a part of Mexican territory. It argues that during the second half of the nineteenth century, residents in the El Paso area—Mexican, Mexican American, American, and Indian—shared in developing a hybrid legal system that brought together Spanish and English languages and cultures, as well as doctrines and procedures from both common and civil law systems, in the local courts. Surprisingly, this unique legal culture persisted for several decades, until the balance of power in the county shifted with the coming of the railroads.

One of the key findings of this study is that the development of American law along the border depended heavily on participants of Mexican descent. For at least three decades, El Paso's juries were made up almost completely of men of Mexican descent. Men with Spanish surnames also were the majority of justices of the peace and county commissioners. This had repercussions not only for their own investment in American law and American citizenship, but also in the ways that Anglo-American lawyers and judges practiced law.

To explore the relationships between citizenship, local law, and federal power, this study looks at the areas of law that were directly related to the development of this border community over time: land law, jury service, the legal profession, the regulation of crime and violence, and the interpretation of international treaties governing the border. It describes the development of local legal institutions, drawing on state and county legal records, but it also looks for law in less familiar places: letters and diaries, newspaper articles, and community petitions, among other places. This expansive focus helps us to see that law was a pivotal element of the larger cultural imagination in El Paso, not just a set of governmental institutions or doctrinal traditions.