Bright bunches of pansies grow in a grassy meadow. They sport classic yellow flowers, decorated with blackish-purple lines. This is Johnny jump-up (Viola pedunculata), a large native violet also known as California golden violet or yellow pansy. Johnny jump-ups are mostly found in the grasslands of western central and southern California, as well as in woodlands and coastal scrub. Unlike many violets, their leaves are ovate rather than classically cordate or heart-shaped.
Johnny jump-ups can often be confused with the much more widespread goosefoot violet (Viola purpurea)–but it has larger flowers (generally 1 to 2 cm), more uniformly ovate leaves, and the expert eye will note that it also lacks the cleistogamous* flowers of the goosefoot.
*Cleistogamous flowers never open, and pollinate themselves. The opposite–a “normal” flower–is chasmogamous; hence, opening (like… a chasm?). There’s a good description and some photos of cleistogamy in violets on this web page.