Can you recommend a good ground cover plant for a slope that is eroding?

The large slope in my yard is eroding. It doesn't really help that there are gophers. I don't have any plants on the slope except for a large pine tree and weeds everywhere. The slope gets a lot of sun. I live in zone 9, or 15. I get different numbers from different sites. Anyway, I live in the San Francisco, East Bay area. I'd appreciate any suggestions and where I can buy these plants.