Transamerica Redwood Park
not the garden variety.
This non-native Oxalis is a periodic escapee from cultivation. These plants have colonized a gravelly creek bed; not particularly invasive.
I had overlooked the proper ID of this flower for several years, thinking it was a native Oxalis. Compare with the endemic Drummond's wood-sorrel, found growing nearby on limestone ledges:
I have three species of Oxalis in my yard; this is the only native species. A Texas endemic!
The Oxalidaceae, or wood sorrel family, are a small family of eight genera of herbaceous plants, shrubs and small trees, with the great majority of the 900 species in the genus Oxalis (wood sorrels). Members of this family typically have divided leaves, the leaflets showing "sleep movements", spreading open in light and closing in darkness.