Tres Hermanos Ranch is a rare glimpse at a pastoral past. But what about its future?

The scene from the perimeter fence of Tres Hermanos Ranch is a glimpse back in time: longhorn cattle and deer roaming green fields framed by forested hills and watered by streams.

Stretching from the 60 Freeway in Los Angeles County south to the western tip of San Bernardino County, the 108-year-old…