The California Legislature had jurisdiction over changes of names from 1850 through 1865. If you are looking for someone, in some cases entire families, and can not find them, you might consider a change of surname as a possibility.
I have transcribed entries found in the law books and newspapers for most years and have a partial database containing several names, which includes some women and children.
Some names are shortened ethnic names, but in other cases the new names are totally different.
This is another place to check, especially if DNA has been done and does not match any surname results.