I am certain that the plant shown by Maurillio is not M. boolii. This has hooked spines and there is no known form of this plant with straight spines. M. sheldonii f. iniae is, as Ento says, found at Bahia San Carlos. Here is one that I saw in April this year.
But in a rather different part of Sonora, I also found some straight spined plants that were not really the same, though I believe them also to be a form of M. sheldonii.
It was a shame that there were no flowers.
Marco's photo is one of these M. sheldonii forms, I think. I have a plant which comes from Bacum, under the field number HK277 which has pale flowers, not unlike Marco's, but my plant has hooked spines. I think this just shows how variable this species is, and how it changes with the different habitats.