First California Financial Group has received final approval from federal regulators for its merger with PacWest Bancorp.

The merger between First California Financial, parent of Westlake Village-based First California Bank, and PacWest, headquartered in Los Angeles, is expected to close on May 31. The conversion of First California branches to PacWest branches is expected to be completed by June 14.

First California Bank, with $1.9 billion in assets, is a 15-branch institution serving Southern California from San Luis Obispo to San Diego counties. PacWest, with $5.4 billion in assets, has 66 branches from San Francisco to San Bernardino counties.

The banks have not indicated if some branches will close in the merger. But both operate branches in Glendale, while First California has a branch at its former headquarters in Westlake Village, near a PacWest branch in Thousand Oaks.

The deal is valued at $231 million and would make the combined institutions the eighth largest publicly-held bank headquartered in California.

Shares of PacWest fell 20 cents, or less than 1 percent, to close at $28.07 on the Nasdaq.