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Opuntia polyacantha - Plains Prickly Pear cactus. The polyacantha species name translates to "many thorns" as can be seen in the photo.
This particular specimen was a roadside rescue from being tossed to the curb in a pile of junk for the city to pick it up near my office. I saw it, grabbed a company van and a dolly and saved it. It has been overgrown in the 5 gallon pot for some time. It's still surviving under my care and will be opening 4-5 more blooms next week as seen in the pic.
I have several of these potted and in ground. They are quite hardy in all seasons of Utah weather and are native in North America from Louisiana to Canada and west to California but excluded from Oregon and Washington states.