"This is the first step," Stine said. "If you wait until you have every answer for every question you never get anywhere."
Under development proposals, he said, about 23,000 acres of the ranch's 28,000-acre mountain resort in Kern County would be dedicated as permanent open space, as would 5,700 acres of the 12,000-acre "new town," Centennial.
In addition, Stine said, the ranch is negotiating the preservation of between 10,000 and 20,000 acres of San Joaquin Valley grasslands under a federal habitat conservation plan. So perhaps 150,000 acres of the ranch could be permanently preserved under current plans, he said.
Of the remaining 120,000 acres, about 12,500 would be developed over the next 25 years, and the rest would remain in traditional ranching and farming activities indefinitely, he said.
Stine downplayed concerns about development in the 5,000-acre Bear Trap Canyon, where he said about 200 homes are planned. "The rest will remain natural open space," he said.
Stine said all three urban projects planned at the ranch are fully financed.
"This is not a capital strategy," he said. "We think it is the right thing to do, and we hope the environmental community will support it."
In a news release, the Trust for Public Land lists support from environmental scientists and activists, including a director of the Pacific Crest Trail, which would be realigned through the rugged backcountry of the ranch.
"The reroute of the [trail] would allow public access and a much-improved user experience in this wonderful region of California," trust Executive Director Liz Bergeron said.
In an interview, U.S. Fish and Wildlife Service spokeswoman Alexandra Pitts also praised the plan as "an excellent model for science-based conservation planning."
Founded in 1972, the Trust for Public Land has functioned as a broker in evaluating sites and arranging conservation deals between private landowners and government agencies.
Holderman said the Trust determined which 100,000 acres to buy -- "the best of the best" -- based on the research of biologist Michael Josselyn.
Josselyn led a team of experts who used overlays of more than 50 sets of data to determine which lands would provide the best habitat for rare species of plant and animals, maintain watersheds and provide connections from one habitat to another.
Included in the preserve is the ranch's wildest backcountry, miles of steep canyons and rugged ridgelines soaring nearly 7,000 feet -- home of California's largest unspoiled oak woodland and the traditional playground of the California condor.
The wildlife preserve would also include a wide, long finger of land that reaches out westward from the highlands core along the grassy foothills to I-5.
The San Joaquin kit fox, an endangered species, occupies this area, as does the rare blunt-nosed leopard lizard and the California burrowing owl.
"Conservation biologists wax poetic about this area," Josselyn said. "It can be managed for a suite of species."