Common. Fully naturalised in scrub along track margins.
Miner's lettuce south of Hoffman Mountain.
San Diego County, California, US
I'm not sure of species. I couldn't list this simply as "genus Claytonia".
Claytonia perfoliata (miner's lettuce, winter purslane, or Indian lettuce; syn. Montia perfoliata) is a fleshy annual plant native to the western mountain and coastal regions of North America from southernmost Alaska and central British Columbia south to Central America, but most common in California in the Sacramento and northern San Joaquin valleys.