Hooker's Evening Primrose (Oenothera elata subspecies hirsutissima) flowers have 4 heart-shaped petals and can be reliably found along reliable water after monsoon rains. Look for them along the creek.
Photo by Carol Tornow, 9/2/11
These plants are now in their own family (of 2) Martyniaceae (Unicorn Plant Family). Both Proboscidea altheaefolia (yellow, above) and Proboscidea parviflora (white) are commonly known as Devil's Claw, but the yellow one is also called Desert Unicorn Plant and, perhaps more conveniently, Golden Devil's Claw. Using the very cool 'Botanary' gives the meaning 'like an elephant's trunk' for Proboscidea. (Same root as your favorite word 'proboscis'.) Seems to me that both the flower and the seed pod fit that description. Carol and I have seen many more of these plants this summer than we did last year. (Might be because we recognize them now, though.)