Can someone identify this brown spider in California
It looks a lot like a Kukulcania hibernalis, or southern house spider. This one appears to be a female and if it were to bite you then it would be painful, but not dangerous. These spiders typically keep to themselves so unless you find one hanging in a really bad place it's better just to leave them alone.

For further information you can look here:

https://spiderid.com/spider/filistatidae/kukulcania/hibernalis/