It is a system that uses few outside resources and could go on and on - if we take care to prevent soil erosion. And pasture is a good land use for these hills. Sheep are easier than cows on the steepest land with regards to erosion. Grazing animals turn plants that we cannot eat, mostly grasses, into food that we can eat and fiber that we can use. Joe and Donna both said that ranchers know and understand their land better than anyone else and generally do a good job looking after it.
Separate pastures mean fence, and fence is expensive.
Sheep ranching is no longer economically viable - that is the problem. Sheep numbers in Sonoma County have declined in thirty years from 130,000 to 16,000. Even locally, where it is too foggy for grapes to oust sheep from the land, as they have elsewhere, numbers have fallen. He considers predators the most serious. The second factor is markets.