I think it's definitely along those lines- I was unable to find a matching wing pattern though. I wonder if it might be a juvenile? I was also amazed at the differences among the pictures for Notonecta. I've been going through some of the comments and they seem to imply that Notonecta are common in the north/north east, not in the south as much.

Adult insects have wings, immatures do not. You have an adult Notonecta there.

With its wings starting to "unfold" for flight in your photo, I can't say for sure, but the difference between N. undulata and N. indica is a black band in the shape of a "W" for undulata and a broad black band for indica.

Could be N. indica.

Backswimmers are common in temporary pools (places w/o vertebrate predators) whether it is in the N or S.

You'd be amazed at the number of aquatic insects, let alone backswimmers in ephemeral pools in desert mountain canyons or valley stock ponds.

Definitely a species of Notonecta. Again, you can't always go by color pattern alone, as there is some individual variation.