What recourse do I have against a tenant who is terminating the lease early?
Typical landlord remedies for tenant breach:
If a tenant breaches the lease agreement, the landlord must serve written notice of the breach upon the tenant, describing specifically what constitutes the breach, and in many cases, stating a deadline by which the tenant must remedy the breach or be terminated. The period of notice prior to the deadline is defined by statute and varies in length depending on the severity and type of breach. If the breach is non-payment of rent, a period from three days to two weeks is typically allowed for repayment. If the breach is related to a condition which affects health or safety, a suitably short period of time is allowed in which to remedy the defect. If the breach involves property damage or other non-threatening conditions, the period of notice is typically 30 days, and the landlord may exercise the option to repair the damages himself if tenant has done nothing within two weeks (tenant being charged with the price of repair).
USLF CA-829LT (California Notice of Default on Residential Lease) may be helpful to you.