Here’s a description from Rich Toyon:
“I do believe it is a Paeonia californica (California Peony). You asked me if it was a California Native and indeed it is. However, it depends on its classification. The common peony (Paeoni brownii) range is fairly vast covering most of the southwest and into northern Mexico but this one is particular to southern California and only the western part.
You don’t see California peony very often because it usually pops up as a somewhat hidden Chaparral understory plant and it only shows when conditions are right. It loves sandy soils and hibernates in the dry hot summers and pops up with intermittent winter moisture. That is the reason it is so hard to grow in a residential setting, summer watering will usually cause the fleshy root to rot and kill it. “