The plant from a distance looked like dandelion but is a perennial and leaves thicker with underside white, forming almost a complete ground cover in many places. Pl. help in ID.
SOLVED: ground cover in SFO Zoo
I think it is Arctotheca; it is a very common invasive weed with many forms. May be A. prostrata.
I felt bad to not accept JasperDale, but I knew A. calendula is an annual weed and this plant was clearly carpet forming perennial. I could not explore any further because this species is described in Online Flora of N. America and Revised Japson Manual of California plants published in 1996. Thanks Vestia for A. prostrata which matches with my plant. I found a big patch of it in Sunnyvale yesterday and luckily it features in Online Japson manual