Catalina and Hollyleaf Cherry (Prunus ilicifolia)
 

Prunus ilicifolia is a species of the Plum family that is native to southern California and Baja California (Mexico). There are two native variants which are very difficult to distinguish from each other unless observed in the wild:

• Catalina Cherry (Prunus ilicifolia var. occidentalis, synonym: Prunus lyonii). Native to the loamy clay soils of the Santa Monica Mountains, Palos Verdes Peninsula, Catalina Island and nearby islands.
• Hollyleaf Cherry (Prunus ilicifolia var. ilicifolia). Native to porous terrestrial soils of coastal-influenced southern CA and Baja Mexico.

and also

• Nursery Stock (Prunus ilicifolia). Those sold in nurseries are typically nth generation plants cultivated from seed or rootings of same and sold under either of the above names. Although often recommended to be grown in porous soils, it's just fine in the loamy clay soils of San Diego county.

The fruits are very similar to cultivated cherries in appearance but the flavor is more reminiscent of cherry plums.

Here's a branch from my plant sporting buds about 8 weeks early

Re: Catalina and Hollyleaf Cherry (Prunus ilicifolia)
 

Here's a picture of the flower buds opening