Methownet BB

Anyone have tips for planting a ponderosa pine? It's a dry, south-facing hillside with mostly sagebrush, and I want a ponderosa in one particular spot. Rocky conditions without much topsoil. I presume I'll need to water it for the first few years. Anything else? Would the local nursery have some to transplant?

Yes the native plant nursery by the interpretive center in Twisp usually has Ponderosa pines in different sizes. They also will be given out at the Arbor Day events in Twisp.
You can get a planting guide from the nursery or Arbor Day events.
Some other tips: water using slow drip or bubbler and soak it for a good while. Sounds like it will not have any shade so watering often when it’s 100 degrees will be a necessity. While the tree is young, protect it with a Fence and stake the wire fence to keep the deer from nibbling on the leader and new shoots but mainly to keep the bucks from destroying it with their horns. Good luck.
Len

Inevitably there is a certain seedling mortality rate, and in our experience it isn’t low. Deer, insufficient water, excess cold, aphids and other insects, root-eating gophers. Consider planting several or many seedlings with a plan to eventually cull back survivors to the one perfect tree you are looking for.

Water is the key. At least 2 years of watering until they become established. If you want them to really grow keep watering. New trees we've watered for 10 years are 25ft tall, ones we didn't are 12 feet.

One trick for better hydration is to bury in the hole when you plant a 3’ or so pvc pipe with perforation holes drilled, fill the pvc with drain rock so the water can get down farther. This works really well with drip systems