What are these marks?

[Brontosaurus]

All our Stenocereus alamosensis have the dreadful looking scab things. Is this scales? I thought scale insect left smaller marks. Thanks!

[hegar]

First of all, I wanted to let you know a little about armored and soft scale insects. Unless the spots on your Stenocereus are smaller than 1/5 of an inch, you are not dealing with scale insects.
It looks like your plant does have larger blemishes, especially near the base. The second image even seems to show pebbles, that are wedged between the ribs of the cactus. Your plant has obviously gone through some hard times. I would go ahead and "clean" it a little, i.e. remove, what I believe are pebbles and also pry a few of these circular scab lesions off. Most likely, the tissue underneath is green and healthy and the dead tissue consists of plant matter. It is just a guess, but your plant may have had a severe mite or insect infestation some time ago, which did cause the dead areas on it.
A few years ago, a blogger posted a short story and images showing just what I see on your images This reader claimed, that the "zits", as he called them are nothing to worry about, because there is healthy tissue underneath. They are thus only a cosmetic problem.
I would only get a little worried, if they do increase in size and number and are becoming established on the upper portion of the cactus trunk.

Harald

[Brontosaurus]

Thanks for the advice! That was all very helpful.