You can't miss them. Big white flowers along the roadside in the eastern Rocky Mountains and out onto the plains.
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| crested prickly poppy, Argemone polyanthemos |
The plant is crested prickly poppy,
Argemone polyanthemos, poppy family, Papaveraceae. It is also called the thistle poppy and, a name I haven't seen in writing but makes it easy to remember, fried egg flower.