Robin,

They're getting cooked (it may be the result of underpotting) - repot it into fresh soil, kind of deepish, or put it in the ground. It's a fine plant for sure, and often classified as a Tephrocactus.

Thanks. It might be slightly underpotted. It's on my list to be repotted so, I know what I will do tomorrow :) I will reduce the sun exposure too to see if I can get this to look beautiful. Thanks again.

Robin,

It's a full-sun plant, even in AZ. It just needs sufficient resources to combat the day. Anything I can do to promote Tephrocactus (pronounced 'Jethrocactus', oddly enough) you can count me in for.

I broke off all the segments and planted the un-scorched ones in a bigger and deeper pot. And of course I planted the ugly ones in a new pot for baby making :) They are back in full sun, but I might give them some shade in the middle of summer.

Thank for your help,
Robin