At the time of the Louisiana Purchase in 1803, California was owned by Spain. The area had been part of Spanish territories since the colonial era when Spain began settling in the region in the late 18th century. However, even before Louisiana was purchased by the United States, California was in the process of changing hands due to various geopolitical shifts.
Shortly after the purchase, in 1821, Mexico gained independence from Spain, which then meant California became a Mexican territory. The implications of the Louisiana Purchase were significant, as it expanded U.S. territory and set the stage for future westward expansion, eventually leading to the annexation of California in 1848 during the Mexican-American War.
In summary, Spain owned California at the time of the Louisiana Purchase, which marked a pivotal shift in North American geopolitics.