|Not a mountain lion either.|
Turns out this is a Tobacco Hornworm (Manduca sexta). Fred writes: "They use many plants in the Solanaceae family and are known to be a pest on tomato plants. Ours had been munching the Datura plant we found him on."
Fatal Metalmark seems a very scary name fpr a common butterfly. Likes seep willow, but is here on desert broom. Photos from Ned Harris from nature walk on 11/10/10. Thanks Ned (and Fred).