| Cover | Sep. 20, 2024 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Sep. 20, 2024 |
| Entity File Number | 001-41684 |
| Entity Registrant Name | California BanCorp \ CA |
| Entity Central Index Key | 0001795815 |
| Entity Tax Identification Number | 84-3288397 |
| Entity Incorporation, State or Country Code | CA |
| Entity Address, Address Line One | 12265 El Camino Real |
| Entity Address, Address Line Two | Suite 210 |
| Entity Address, City or Town | San Diego |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 92310 |
| City Area Code | (844) |
| Local Phone Number | 265-7622 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock |
| Trading Symbol | BCAL |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | true |
| Elected Not To Use the Extended Transition Period | true |
