Well, I'm pretty sure it was a gopher. I went to look around the base of the plant, and it was gone. The whole base of the plant was gone:
[img]https://dl.dropbox.com/u/3552590/PumpkinRemains.jpg[/img]
I couldn't even tell where the roots had been.
Then I looked around the garden and saw a drooping sunflower, and its base was submerged in a hole
[img]https://dl.dropbox.com/u/3552590/MurderedSunflower.jpg[/img]
The bottom of the stem looked pretty grim:
[img]https://dl.dropbox.com/u/3552590/MurderedSunflowerDetail.jpg[/img]
A few days later I was about 10 yards away, and I heard a "crunching" sound. I turned around and watched some scrub brush being pulled backwards into the earth!
I think I'm going to amend my signature.

Sunset 23/USDA 11a, Elev. 783', Frost free since 8,000 BC. Plagued by squirrels, gophers, and peafowl, but coming to terms with it!