I saw this cactus in Tucson AZ April 2024 and was amazed by the "pelt of fur" it had grown. Within the fur there are dried flowers. It was a single straight tree about 6 foot tall. Any ideas what the fur is and what type of cactus it is?

Cephalocereus species? The most common species in cultivation is C. senilis, but I'm not sure that's right.

The weird furry part of the cactus is called a cephalium. It develops only once the plant has reached maturity (flowering size) and only along part of the stem (often the side facing the sun). It is where the flowers appear. The hair in the fur is a modified spine.

If you are wanting something like this in your own garden, C. senilis is relatively easy but it does take a while to reach maturity and start making a cephalium. There are other species and genera that also make cephalia, usually with a sort of furry/hairy look, mostly less common and sometimes more difficult than C. senilis.

Thanks Baja, I'm forever trying to learn more botany. Plants are amazing. I read a little more on this website, lots of good photos:
http://www.sbs.utexas.edu/maus...
Thanks 2Traveln for a good question and photo. Welcome, and be sure to check out the Cactus and Succulent Forum!

Very interesting page you found there.

Our database page on C. senilis is here, for what it's worth

Old Man of Mexico (Cephalocereus senilis)

and here are pictures I took in habitat of a different species