I second Baja! P. marginatus for sure.
Here is one of mine:
When they have a good source of water and well draining soil these things can get gigantic.
Unfortunately I do not have a good picture, but the tallest stem that you can see in the picture doubles in thickness about halfway down - that was its growth habit when I got it. A friend had grown that next to a patch of roses that got very regular irrigation. The thing was easily two and half stories tall and that is what did it in: a big monsoon storm and it came crashing almost took out his car. I got the top 3 or so feet of it. It gets a lot less water from me so it is not continuing its thick/quick growth, but doing quite well nonetheless. They do get tippy when tall.
These should be able to take 9a I think, they take 9b without a problem for sure... My photos are not organized enough to post a pic of its flowers, mine have never flowered, but I have seem them in flower in the Desert Botanical Garden in Phoenix.
The cactus on the right is one of its cousins: Pachycereus pringlei, those are more frost tender than P. marginatus.
