quarterboredave - thanks, that was exactly the type of answer I was looking for!
VarmintGuy - must be a regional thing; all types of ground squirrels are called whistle pigs or sage rats here. Rock Chucks are called chucks. At least that's what everyone I know around here calls them...
The little ones are Beldings Ground Squirrels -
http://www.mnh.si.edu/mna/image_info.cfm?species_id=354 . Like you say, a centerfire is a bit much on these. A 22 with Aguila Super Maximum Hollow Points works great and is a lot cheaper than a 17 HMR.
The bigger ones are Columbian Ground Squirrels -
http://www.mnh.si.edu/mna/image_info.cfm?species_id=354 . These are about 2/3rds to 3/4trs the size of a prairie dog. With the 50 grain Vmax they just kind of hump up and fall over.
Now to find some bullets; Cabelas and Sportsmans are both out of the Hornady SPSX. Might have to order them...