The US- Mexican relations would be interesting in this situation. If the US is able to take all of the Oregon Territories from the British in 1846, the US might not be as interested in California as in our TL. That would change after the discovery of gold. I can see a Mexican- American War in the late 1860s early 1870s. The US would probably win and take all the land west of Santa Fe, all of California most likely including the Baja peninsula.
Of special interest is the Mexican population in the 1840s in California. It was nearly as sparsely populated as Texas before the Anglo-American immigration of Texas. I've seen one source that put Mexican population around 3000 and about 10000 natives. Other sources put the total of the two at 8,000. There wasn't much love lost between the Mexican settlers in the region and the central government in Mexico City.
There's an argument to be made that within a year or two of gold being discovered, American immigration would effectively swamp the existing population completely. Then something similar happens with California as what happened IOTL with Texas.