I've tried to identify this cactus since I acquired it, and I'm still not sure what it is. Two folks that I consider cactus experts have given me their opinion that is was an Echinopsis, and for a while, I thought I finally had the answer.
Recently, I sent two photos to the Desert Botanical Garden for help with identification, and as an afterthought, sent along an earlier photo of this cactus in bloom, but with the cactus body showing. They believe it is of the Echinocereus genus, species unknown. So, who knows? And really, what does it matter?