Why was california not considered for statehood before the gold rush in 18 48?

After the Portolà expedition of 1769–70, Spanish missionaries began setting up 21 California Missions on or near the coast of Alta (Upper) California, beginning in San Diego. During the same period, Spanish military forces built several forts (presidios) and three small towns (pueblos). Two of the pueblos would eventually grow into the cities of Los Angeles and San Jose. After Mexican Independence was won in 1821, California fell under the jurisdiction of the First Mexican Empire

It was a combination of conquests and alliances