I thought I mentioned it in this thread already. California state law allows for a notice to pay or quit on the day rent is due if no rent is paid. This notice allows the tenants 3 days to either pay, or leave the property, If they refuse to leave then they will receive an unlawful detainer. They can challenge this which will allow them to stay another 30 days, however they then must make court appearances and could pay a fine or even get arrested in some circumstances.
Trust me, I wouldn't be stressed if I didn't know how annoying these things are.