Echinomastus erectocentrus v. acunensis, exactly where they said it would be.
So I became obsessed with the above rare Arizona endemic, in one of those genera that features a very few species almost all of which are obscure and occupy fairly restricted niches. The genus is Echinomastus, which certain cactus conservatives have recently sunk entirely within Sclerocactus, thus effectively removing the distinguishing characteristics of both genera. (The degree to which I can be incensed by recent boneheaded renaming is remarkable, but I have perhaps wisely avoided ranting about it here....)
It took me three nearly full days of searching over the Thanksgiving holiday to find two plants. I found this population at the very end of the third day, near sunset.
Part of the fascination is actually that the low Sonoran desert doesn't really have all that much biodiversity, botanically. The plant species that have adapted here have adapted extraordinarily well, to the point where there's a kind of formulaic monotony to the botanical situation. Sometimes huge areas are stunningly massed with dense cactus forests, but quite often this represents the great success of about 5 species. So it fascinates me that this well-camouflaged, highly restricted plant is also present.
The other aspect that got me obsessed was to see a plant that taxonomists don't even recognize as existing. The somewhat more common, though also rare, Echinomastus erectocentrus has largely survived the recent taxonomy by the blind absurdity (except for being called Sclerocactus erectocentrus). But ssp. acunensis has disappeared from "recognized" lists, in the aftermath of Mr. Magoo rewriting the books on cactus systematics.
Anyway, I had the GPS navigator with me and got coordinates so I can pretty much get back any time, without former long hours of searching. It's cattle country, and very accessible to people out ramming around on ATVs, so it'll be interesting to check in periodically.
This brief interlude brought to you from the cactus side of things...back to Rex Harris and 55 year old jazz purism soon.