A mention of the Diablo Range in the Tri-Valley is likely to draw the response: "What range? Do you mean Mount Diablo?"

Mount Diablo is the northern peak of the Diablo Range, which begins at the Carquinez Strait, runs south to include the Altamont Pass near Livermore and Mount Hamilton east of San Jose, and continues through 12 counties for a total of 150 miles to the Antelope Valley. Its highest peak, San Benito Mountain, reaches 5,267 feet.

These vast mountains, hills and valleys are often not recognized as the Diablo Range even as residents traverse them via the Altamont Pass and Pacheco Pass en route to Interstate 5, where the range serves as the backdrop in the West for motorists to Southern California.

"It is a rugged, remote, difficult realm, a biodiversity ark incised by the San Andreas Fault," summed up Eric Simons in Bay Nature magazine, Spring 2020, in an article titled "The Spine of California."

Outlaws such as Joaquin Murieta took to its ridges in the 1800s to escape lawmen, and now intrepid naturalists rely on 4-wheel vehicles and sturdy walking shoes to search for endangered species.

"Part of its biological wealth comes from its geology, specifically massive deposits of serpentine rock that 30 to 140 million years ago formed on the seafloor and were then lifted up to form the fractured peaks and bandit-friendly fastnesses of the Diablo Range," Simons wrote.

Seth Adams, land conservation director for Save Mount Diablo, now also focuses on other parts of the Diablo Range.

"The major difference is that north of the Altamont Pass, we've protected 75% of what's important," Adams said, "and in the rest only 25% has been protected."

The Diablo Range comprises anywhere from 5,400 to 10,000 square miles, Adams said, depending on whether one defines it from where the land begins to rise quickly or by the rivers or streams on either side.

"Up here in the East Bay, for political reasons, we drew it based on Mount Diablo and it starts at the Carquinez Strait," he said. "All of the hills in the East Bay are part of the Diablo Range."

Adams noted that the Diablo Range is intact biologically, with only two major highways crossing it -- Altamont and Pacheco passes -- and little cell phone coverage.

He and wildlife biologist Joseph Belli, author of "The Diablo Diary," have begun to meet monthly to search for rare and endangered wildlife in the Diablo Range. Recently they visited the Panoche Valley to look for the blunt-nosed leopard lizard.

"He's my guide to much of the Diablo Range," Adams said. "In the Panoche Valley on a recent Friday, we had a search list of five endangered species and found three. When you go out with him, you will find all sorts of cool stuff."

Belli, 59, grew up next to open space in the foothills of Mount Hamilton, where his father ranched cattle. He moved to a 55-acre parcel along Pacheco Pass in 2005, and shortly afterward began to write essays related to his experiences in the Diablo Range.

"I started out in 2006 when I had this overwhelming urge to write about horned lizards," Belli said with a laugh. "I am influenced by essay writers and saw myself writing it and sending it out to a couple of friends."

The feedback was encouraging.

"I started writing about other critters, with a different angle than you would get in a field guide," Belli said. "I found myself going beyond writing about the animals, starting to talk about issues. In my later writing, I started to become a little more esoteric, writing on human nature and nature -- the critters were foils for writing about life in general."

"Years later, it turned out I'd written 25 of the essays," he added. "The last writing was in 2013, and there have been several detours along the way."

The detours included Belli earning his master's degree in conservation biology from San Jose State University, and documenting breeding amphibians (California red-legged frogs, California tiger salamanders, western pond turtles and foothill yellow-legged frogs) in the ponds and streams from the five watersheds in Henry W. Coe State Park, a project that took seven years.

In 2017, he published the 25 essays as "The Diablo Diary."

"I'm a big fan because I like good writing," Adams said. "He does a good job in describing the wildlife and the science and weaving in his personal experiences. And he has a great sense of humor."

"It has a wildlife focus but also a sense of place," Adams added. "He is the best kind of passionate -- an obsessed person who is going to spend hundreds of thousands of hours chasing down tule elk."

"The Diablo Diary" inspires love for the wilderness that is the Diablo Range and traces threats to critters great and small, including mountain lions, California condors, tule elk, California tiger salamanders, San Joaquin kit foxes and horned lizards.

The essays also address environmental issues, including the controversy when the company Solargen proposed putting several million solar panels in the Panoche Valley in 2009. Three environmental groups charged the project would hurt native species; eventually it was cut by one-third and is now a 1,300-acre solar farm.

The range is endangered by suburban sprawl, energy development, proposed dams and reservoirs, plus the California High Speed Rail plans to cut across near Pacheco Pass, but the biggest threat, Belli says, is non-native species, some introduced on purpose by clueless individuals. One essay includes the following:

Pop quiz: which of the following species currently inhabiting the Diablo Range are not native: opossum, red fox, wild pig, bullfrog, bluegill, largemouth bass, wild turkey, house sparrow, starling, eucalyptus, tree of heaven, yellow star thistle, field mustard, poison oak?

Answer: all but poison oak.

Perhaps the most poignant chapter is "Once There Were Bears," four words that sum up the tragedy of a grizzly bear population, estimated to have been around 10,000 before the Gold Rush when grizzlies shared the land with the Native Americans as both sought salmon and acorns as their main diet. Now the grizzly only lives in California on the state flag.

"I love the Diablo Range with the kind of hard-earned emotion that can only come from decades of familiarity with the land," Belli writes, in lamenting the extermination of the California grizzly. "I've seen its great creatures, from mountain lions to golden eagles; in recent years, I have marveled at the return of elk, pronghorn, and condors. Yet there was always something lacking, some element of missing grandeur that would revive the glory that was once present."

Belli's next book is on the California condor, which has a wingspan of more than 9 feet, and is, as he says, "arguably the most spectacular bird in North America."

He volunteers with the condor conservation program at Pinnacles National Park; although condors were gone from Northern California by 1900, a captive breeding program has brought them back.

"It's been a big part of my life the last 11 years," Belli said.

He is currently working with an illustrator to produce the new book, which will benefit the Pinnacles Condor Fund.

Early Spanish explorers were the first to write about their adventures in the rugged Diablo Range. "Clyde Arbuckle's History of San Jose" noted their confusion in 1776 as they traveled the range southwest of what is now the Altamont Pass, doubled back, and tried to find their way around water and marshes.

"But on traversing the high, rough country ... they felt that the range had played a joke on them, and their Spanish sense of humor persuaded them to name it 'Sierra del Chasco' -- 'Range of the Joke,'" Arbuckle wrote.

In his Bay Nature article, Simons honored the past of the Diablo Range and predicted what is to come: "It is a historic mixing place, where Central Valley Yokuts and coastal Ohlones traded and danced, where California's ever-more-diverse future residents will seek escape and recreation."

Explore the Diablo Range

* Visit Mt. Diablo State Park. Save Mount Diablo offers programs to help visitors appreciate what they are seeing; go to www.savemountdiablo.org.

* Drive Mines Road off Tesla Road in Livermore, 30 miles of rugged scenic views.

* The highest peak is San Benito Mountain; the drive requires a 4-wheel drive vehicle and permits from the U.S. Bureau of Land Management.

* Once a year, Henry W. Coe State Park opens the road into the Orestimba Wilderness. Learn more at coepark.net/bcw.

* Coyote Ridge Open Space Preserve in Santa Clara County lists events at openspaceauthority.org.

--Information from Bay Nature magazine, Spring 2020