Way south of the border, namely, Patagonia. To be precise, Argentina. This is Pterocactus tuberosus.
These are funny little things, with large underground tubers and (I think mostly) annual stems, and huge flowers. I only know this from reading the wonderful book A Cactus Odyssey, one of the few plant books I’ve read more than twice.
My experiences with plants from the Andes have not been hugely positive. Most of the alpine plants, while winter hardy, hate the hot summers here. Maybe I should be growing them upside down. (Don’t worry, it’s subtle.) I’ve never gotten into the Andean cacti to any great extent (this means they mostly died, and I gave up), though I did grow the cactus-with-leaves Maihuenia poeppiggii for years, until ants decided to build a hotel underneath it. It hasn’t been replaced, but should be. I would also like to have M. patagonica, but try finding that anywhere, except in Patagonia.
Last year I grew a tray full of gymnocalyciums that have proven to be hardy here in other gardens, in very gritty “soil”, on the patio out in the far corner of the yard, where they were covered in snow for three straight months, thanks to the shade provided by the fence on the south side. All of the cacti were mush by the time the snow receded. Mush is bad.
On the other hand, the delightfully wicked Maihueniopsis darwinii endured the same conditions, and see how it turned out. Maybe the snow was afraid of it. I know I am.