Beautiful plant, but be very careful. It can be extremely difficult to remove from unwanted areas. A raised border planter won't necessarily be sufficient to contain spread--it can send rhizomes down and then laterally. (Picture down a raised planter and under a 3-4' concrete walkway.) If brave enough, I would put it in a solid bottomed planter with just drainage holes below, on top of solid concrete. And then be very careful with the pruning pieces. Definitely do not reuse the soil. I love the look of the plant, but don't dare introduce it into my CA garden.

Yup, agreed on the ID. You could probably take cuttings a few nodes long & pot them back into mother plant's pot, to make it look even more full & lush.

If you let it go to seed it will be all over your garden.

Likely Oenothera biennis. If you look around there are probably some first year non flowering rosettes.