I hiked out on a mid-June day along Mitchell Creek; it still bubbled and flowed all the way from is high mountain source to the picnic grounds at the entrance. I remembered previous spring seasons when it had been reduced to a series of still pools by April. I stopped by the alder grove. Now dead, its beautifully proportioned smooth gray trunks once graced the canyon at the confluence of Mitchell Creek and the stream feeding in from Uncle Sam Canyon. One of the dead alder trunks had fallen into the crook of a vital-looking maple sapling, bending it over to the ground. I picked up a straight, strong stick from the creek bank and pushed the dead trunk off of the sapling. The relieved maple sprang up straight, shaking off drops of dew. It was here I felt like a witness to the chaos of changing conditions that is one aspect of nature. And I contemplated how our own lives mirror that. We too, are biological organisms caught in the chaos, wishing for a stability, a balance in nature, that we don't always find there.

From the Walnut Creek BART station, the foothills of Mount Diablo crest and roll away like huge ocean breakers crashing at the base of the mountain. The undulations of these elevated ridges of sandstone and shale provide a visual and metaphorical reminder that there was, at one time, a sea in this valley before Diablo (Ojompile to the Miwok Indians) rose to overlook it. In one of the uplifted strata, a marine layer called the San Pablo formation that looms above the busy streets of town, there are giant oyster shells from a 12 million year old sea bed. Were we to take ourselves back in time to that Miocene epoch of 12 million years ago, the shallow inland San Joaquin Sea would be lapping against a beach we now call the Domengine sandstone. Backtracking this far into the deep past, the piercement of sea floor and mantle rock that we call Mount Diablo has folded itself back into the ground from where it punched through just before the Ice Age.

The mid-Miocene time we are contemplating was an era of rolling grasslands that had replaced the tropical forests of earlier times. Herds of an early type of horse, Merychippus, may have grazed by the San Joaquin Sea, looking up curiously to the opposite western shore whenever the volcano (at a spot we now call Round Top in the Berkeley Hills) poured forth ash and lava. The pebbles of black volcanic glass called obsidian may have washed up on the eastern coast from that source.

Moving forward in time just a few million years, we reach the Pliocene epoch. The San Joaquin Seaway has retreated. We might now hike up a small canyon where a stream ancestral to our present day Sycamore Creek once flowed. There are swampy areas of willows and tules, and beyond the river bank there is the now familiar (and now endangered) savanna of Oak trees and grass. The climate has gradually begun to grow more arid. A chain of volcanoes far to the north, the Cascade Range, has risen up and cut off the flow of moisture-laden clouds into the Bay Area. A new flora of savanna and chaparral has migrated into this drier area from the Sierra Madre of Mexico and deciduous hardwoods have died off in large numbers. But they maintain their hold east of the Rockies where such hardwood forests still stand.

Hiking up "Sycamore Creek" in this early to mid-Pliocene epoch, we might stop to watch quietly a family of Mastodon, an early type called Gomphotherium, as they feed along the stream, browsing on the river bank shrubs, and ingesting the large amounts of water-plants that they need to sustain their elephantine bulk. A saber-toothed cat, Machairodus, or perhaps Ischyrosmilus (known from fossils in Kern County) stalks one of the baby Gomphotherium. But its mother and one of the aunts charge the cat; they gather the baby back into the protective fold of the fancily. Machairodus skitters off swiftly up the bank, casting rueful looks backwards. On the grassy savanna, this svelte cat spots a herd of four-horned antelope, Syndoceras. He creeps up slowly on the grazing beasts. But they pick up his scent and bolt for the open valley. Machairodus chases--falls back. They are too swift for him.

It is high noon. The panting saber-tooth seeks the shade of an oak grove. He meanly peruses a group of swift-running horses, Hipparion, heading for the mouth of the canyon. But he cannot summon up more than a mild interest in tackling this new opportunity. There is always tomorrow-possibly a better day to hunt.

Fossils of creatures like Gomphotherium and Hipparion have been found on the site of the old Blackhawk Ranch and are now on display in the U.C. Berkeley Museum at Blackhawk. We use the fossil record to imagine and recreate the changing scenes of Earth's animal life, and to decipher the mechanisms, of evolution. Following the demise of "Pliocene Park", there came the beginnings of the Ice Age (known as the Pleistocene epoch) about 1.5 million years ago. Large, hardy animals who had evolved in cold isolated pockets to the north found that conditions favorable to their mode of biological survival had spreading continent-wide. These cold weather animals radiated out across North America, many crossing the land bridge from Alaska, and they arrived to dominate California's plains and mountains.

Mount Diablo emerged during this period and, though it was never occupied by an alpine glacier as the nearby Sierra Nevada was, it undoubtedly wore a mantle of ice and snow on its peaks throughout the winter. Herds of Columbian Mammoth with crisscrossed tusks and their huge sets of teeth fully adapted to a diet of Central Valley prairie grass moved from the north, edging out Gomphotherium who was unable to compete for food in the more rigorous colder climate. A new type of saber-tooth, Smilodon, roamed the Black Hills near Sycamore Creek. More muscular and heavy set than the earlier cats, Smilodon moved more slowly but was better adapted to prey upon larger beasts like Mammoth--and Megatherium, a ground sloth who entered California from South America across the Panama land bridge.

Such sudden mutations of new animal forms that succeed and quickly radiate out to rule large territories have occurred frequently in the fossil record. The paleontologists, Stephen Jay Gould and Niles Eldredge, put forward their theory of punctuated equilibrium to explain the series of rapid modifications followed by the stabilization and persistence of the most adaptive forms. The fossil turtles of Mount Diablo show how little change a successfully adapted creature will manifest. The Western Pond Turtle has retained the same features over the million or so years it has occupied Diablo's ponds.

The horse was once considered the exemplary line of an animal showing a progressive, and gradual evolution. The fossil record shows that Pliohippus, the Pliocene descendant of its Miocene ancestor, Merychippus (who browsed by the shores of our once broad San Joaquin Seaway), is one of his larger descendants. However, Nannippus and two smaller types of horse also evolved from Merychippus, demonstrating that a progressive increase in size was not the rule. In Stephen Gould's view, many physical varieties arise, some are winnowed away by conditions that don't support their form of adaptation, and others succeed and continue in a stable, non-progressive form for centuries. If there is progress taking place in evolution, it is not happening in the linear fashion once believed.

With the end of the Ice Age, many of the well adapted creatures died out--this with the help of Stone Age Paleo-Indians who had evolved a hunting culture and weaponry about 12,000 years ago at the end of the Ice Age. In more modem times, records document how the Hudson's Bay Company's traders hunted elk as far south as Mount Diablo-and probably hunted them to extinction to satisfy a fondness for elk skin gloves that were fashionable on the East Coast.

Now Mount Diablo has a new purpose: to protect animals from the extinctions brought on by humankind, and to preserve the Earth's creatures for future generations to enjoy. The mountain lions have come back, and soon perhaps, too, the elk and the pronghom antelope.

Dave Holt - 1993

Drawing: Syndoceras, Miocene antelope, leaping into the open savanna of San Ramon Valley eludes an attacking saber tooth -- by Chappell Holt