What significant event occurred in California in 1848 related to territorial changes?

The Treaty of Guadalupe Hidalgo, signed in 1848, marked a pivotal moment in California's history as it concluded the Mexican-American War. This treaty resulted in a significant territorial change, whereby the United States acquired a large portion of what is now the Southwestern United States, including California. This event set the stage for California's subsequent integration into the United States, influencing its political, cultural, and economic development.

While the discovery of gold on the American River also occurred in 1848 and led to a massive influx of people during the Gold Rush, the treaty itself is key in terms of official territorial changes. California's admission into the Union happened later, in 1850, and the issuance of bonds for the Owens Valley project pertains to a much later period in California's water management history. Thus, the signing of the treaty is the most significant event related to territorial changes in California during that time.