Although the issue of water allocation and management in California has frequently been researched, the origin of the legal, political, and social constructs surrounding the initial stages of development of these regimes is often overlooked, despite their persistent effects on current water policy. The Colorado River and the San Joaquin/Sacramento River complex are the two largest river systems serving California. As a result of greatly differing climates- arid in the south and Mediterranean in the north, settlers adopted different bodies of law-agrarian and riparian respectively. While these laws were the earliest forces governing the management of the rivers, they were not the driving forces behind the creation of the management regimes whose legacies endure today. At the turn of the 20th century, the Progressive movement was sweeping the nation. Both northern and southern Californians utilized the tenets of this movement, adapting them to their own contrasting situations. Those in the south became leading proponents of the reclamation movement, arguing for large-scale diversion to support comprehensive irrigation in an otherwise dry, inhospitable land. Settlers in the north, coping with the legacies of hydraulic mining, utilized conservation to garner support and funding to control floods and manage irrigation of the fertile Central Valley. This paper uses primary historical documents to explore the attitudes and motivations of the politicians and settlers to understand the development of these two differing management regimes. By understanding and examining the past, more insightful perspectives and more coherent comprehensive water policy can be developed in contemporary California.