Cylindropuntia acanthocarpa AKA buckhorn cholla is not exactly a pretty plant. It grows as a large thorny bush with loose branches, stem segments sticking out in random order, and common in southern and central AZ deserts. Flowers are very bright, and range from yellow through orange to vine-red in color. Plants with different flower colors usually grow next to each other.
Note that this pictured flower is horizontally asymmetrical in shape. The upper petals (not 'true' petals from the plant morphology perspective of cause, more like meta-morphed leaves) are fully open, but lower ones are half-open, forming a cup shape. Flowers that occur at stem tips and look more upward are usually fully open and perfectly funnel shaped.
That cup shaped flower bottom is to keep the pollen that falls of the anther, inside the flower. Cacti as many arid land plants produce relatively small amount of pollen, and they sure benefit from such pollen-saving features. Many Opuntoides have such flower shape adaptations, as well as some Echinocerei.
Picture is taken near Wickenburg, AZ