Zions Bancorp said Thursday it has received final regulatory approval to acquire The Sumitomo Bank of California.

Zions and Sumitomo agreed to the merger March 25 and Sumitomo shareholders approved it July 28. The transaction is expected to be completed on Oct. 1. Zions said it expects to merge Sumitomo with its existing bank subsidiary in California, Grossmont Bank, which will be renamed California Bank and Trust.The new entity will be the fifth largest bank in California.