What is your watering schedule for them?

Boy, those are two tough-to-kill plants. I'd bet you could set Rosemary on fire and it wouldn't die. As a general rule, browning from the outside in is not enough water, from the inside out is too much water. Most xeriscape plants must be allowed to dry completely between waterings.

The Creosote had been watered about once a week initially, and now gets a splash about once a month beyond the lack of natural watering that occurs in Phoenix. The Rosemary was heavily watered once a day for a two days, missed a day and by the third or fourth day was getting a significant amount of the burn look.

Probably the most perplexing plant was a bottlebrush tree that appeared to have dried out entirely and has since recovered almost all of its leaves while continuing a once every two weeks watering schedule.

There was a part of me that wondered whether it could possibly be soil salinity or something in that respect.

I didn't think it was possible to overwater in most of Arizona. You may have proved me wrong. Where in AZ do you reside?

How long did it take to drain those planting holes?

Did you add any amendments when you planted them?

Yes, a soil test may prove useful. I am bothered by the speed at which you state the collapse is happening.

You don't need to water Rosemary hardly at all, even in summer, though it will look better and grow faster if you do water in summer. Are these new or established plants you're discussing?