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Hyles lineata
I thought this was an awesome caterpillar! Cool little spike on its back!
Wyoming big sagebrush, rabbitbrush and various grasses and herbs.
That's my best guess at this time. The caterpillars of this moth are incredibly variable, so take a look and see if you think it matches up.
It's definitely the larva of a sphinx moth but I'm still looking through field guides to work toward an ID.