We are in Northern California. If I get off an 8 hour shift at 6 am and then start another 8 hour shift at 2pm (8hour break) should my next shift be considered overtime? I might add this is a 24 hour operation (hotel)

It depends on when the hotel considers its workday to begin- they can pick any time, so long as it is consistent.

In your case, they might have the day begin at 6:00am, so they don't have to pay you overtime. On the other hand, if their day begins at 12:00am, you would work 12am-6am straight time, 2pm-4pm straight time, then 4pm-8pm time and a half, and then 8pm-10pm double time for time over 12 hours in one day.

Hotels are the worst schedulers when it comes to short turn arounds. I believe the minimum time between shifts is 8 hours. Possibly a more senior member can confirm this.

No Alex, there is no such law in California or any other state, except for limited types of jobs for and for public safety reasons, such as airline pilots and over-the-road truckers. I believe you have been misinformed.