Direct answer: a 10 day self-quarantine is strongly encouraged. It doesn't seem to be legally mandated anymore, since the Regional Stay at Home order was lifted on Jan 25th.
That being said,
California Department of Public Health and CDC strongly discourage tourism or recreational travel.
From Official California State Government sources: https://covid19.ca.gov/travel/
Traveling into California from other states or countries for tourism or recreation is also strongly discouraged, and anyone traveling into California should self-quarantine for 10 days, unless quarantining is impracticable and the travel is for the sole purpose of meeting critical healthcare needs or other emergency response
California Department of Public Health travel advisory states: https://www.cdph.ca.gov/Programs/CID/DCDC/Pages/COVID-19/Travel-Advisory.aspx
Non-Essential Travel [I]
Except in connection with essential travel, Californians should avoid non-essential travel to any part of California more than 120
miles from one's place of residence, or to other states or countries.
Avoiding travel reduces the risk of virus transmission, including by
reducing the risk that new sources of infection and, potentially, new
virus strains will be introduced to California.
Non-essential travelers from other states or countries are strongly discouraged from entering California, and should adhere to
the quarantine procedures set forth in Paragraph 3.
All persons arriving in or returning to California from other states or countries, should self-quarantine for 10 days [ii] after
arrival, except as necessary to meet urgent critical healthcare
staffing needs or to otherwise engage in emergency response.
Additionally, this recommendation does not apply to individuals who
routinely cross state or country borders for essential travel [iii].
A Local Health Officer may determine if and when the situation within
the Local Health Offficer's jurisdiction warrants measures that are
more restrictive than this statewide order, and retains authority to
implement such measures.
From CDC's online Travel Planner tool (last updated 2020-12-31):
People arriving from out of state to hotels and lodging entities must quarantine at that facility for at least the 10-day minimum recommended quarantine period
I'll leave you with the CDC's guidelines for travel during COVID-19: