Arctostaphylos uva-ursi?

Arctostaphylos uva-ursi, aka bearberry, aka kinnickinnick. It's a manzanita relative, and is native to California -- as well as planted in the garden.

Cortoneaster horizontalis I would say. If we could see the plant's habit it would help. But the berries appear to be Cotoneaster.

Yes, a cotoneaster. According to the Fryer/Hylmo cotoneaster book several species are grown as C. horizontalis.

The berries are the least obviously different part from those of Arctostaphylos uva-ursi, starting with the leaves.

COtoneaster - obviously. Sorry. I don't know the Arctostaphylos so could only really go on the berries as definite from pictures.

Note that the Cotoneaster horizontalis mentioned can get knee to waist high over time, whereas bearberry will stay more of a ground cover. The berries of both plants are not tasty. If low groundcover is your desire, find an exact replacement or try cuttings or perhaps seedlings.

Best way to propagate Cotoneaster is by layering. Put a brick or a rock on one of the low branches so it is in contact with moist soil, wait a year, clip off from the mother plant and then replant it where you want it to grow.