Ellen Morris Bishop

Once upon a time, when dinosaurs roamed Montana and pterosaurs ruled the skies, there was no Oregon. In those days, more than 100 million years ago, Pacific waves broke on Idaho shores. McCall, 50 miles east of the border with Oregon, would have been a seaport, and Boise a coastal town. The Pacific Northwest was yet to be born. The oldest rocks of Oregon lay far offshore, gathering as coral-fringed islands in a shallow tropical sea.

Oregon's most ancient rocks are almost 400 million years old. They developed in a Devonian world where armored fish patrolled the waters and amphibians pioneered the land. If we had flown past the Devonian Earth in a spacecraft we might not have recognized our blue planet as home. The Earth's continents clustered in the Southern Hemisphere. North America embraced Europe. Gondwana — the southern continent that included Antarctica, India, South America, and Africa — straddled the South Pole. There was no Atlantic Ocean, and the ancestral Pacific, an ocean known as Panthalassa, stretched two-thirds of the way around the globe.

Oregon's most ancient bedrock occupies the Blue Mountains and the Klamath Mountains. It once was ocean bottom, shallow-water coral reefs, and a variety of volcanic islands far from North America's abbreviated coastline. There was no Oregon until plate tectonics cleaved North America from Europe and northern Africa, and moved the continent westward to collide with these reefs and islands, and the disheveled seafloor that held them.

The fragmented islands, coral reefs, and volcanoes now sequestered in Oregon's remote mountains once resembled the modern cluttered seas of Indonesia. They were added to the main landmass from 150 million to 90 million years ago by collisions with an opportunistic continent that gathered orphaned landscapes from an island-dimpled sea and claimed them for its own. North America's western coast, Oregon included, is a collage of exotic geology swept onto the prow of a westward-moving continent like pond scum on the bow of a giant canoe.

It has taken us a long time to understand Oregon's beginnings. Until the dawn of plate tectonics and the revelation that seafloors move and continents collide, geologists who mapped the Blue Mountains and Klamaths labored mightily to conjure order out of seeming chaos. They employed masterful strategies to explain the puzzling patchwork of Oregon's oldest landscapes: why, in the hills north of Burns, shallow-water Devonian limestones lay placidly adjacent to Permian deepwater cherts, or how, in the Klamaths, mangled gabbros intruded into orderly beds of shale. They invented vast and complicated folds to justify a disheveled stratigraphy. Before plate tectonics, there was no mechanism to account for the rumpled, random order of things.

Oregon geologists have mapped the Blue Mountains and Klamaths with painstaking accuracy. Today, some of their pre-1970 explanations for how rocks were folded and faulted into place seem oddly contrived, but they were the only logical explanations then. One memorable example of someone who valiantly tried to comprehend plate tectonic-induced chaos using conventional folds and faults was a capable petroleum geologist named Harold Buddenhagen. In the early 1960s, a decade before plate tectonics would become fashionable, Buddenhagen mapped the contorted geology along Grindstone Creek and in the vicinity of Suplee, open landscape in the navel of the Blue Mountains. His detailed work shows each stone in its proper place, each slanting outcrop dipping into the Earth at precisely the proper angle.

But in Buddenhagen's world, sediments accumulated in tidy, stratigraphic layers and were deformed in a systematic manner at a later time. He could not envision subduction zones mashing neatly stacked sediments into wads of tight folds, or imagine chunks of Devonian limestone slapped carelessly next to Pennsylvanian sandstones 100 million years younger, and the whole jumbled mess slipping into a trench only to be metamorphosed and regurgitated 200 million years later. He interpreted the welter of rock ages and orientations as best he could. His map depicts the locations of each rock with excruciating accuracy. But Buddenhagen's interpretations of contorted plunging folds and concealed faults that moved layers of rock for tens of miles were imaginative leaps of faith in pre-plate tectonics geology. Within a decade, explanations that had made complete sense in a world without plate tectonics, subduction, and accretion would seem as absurd as modern explanations of colliding islands and landmasses would have seemed in the early 1960s.

Despite its accuracy and the encouragement of his peers, Buddenhagen never published his exquisitely detailed and accurate map of the area around Grindstone Creek. Instead, he simply filed a copy with the Oregon Department of Geology and Mineral Industries, where it sits today in the agency's library. In 1966, when he completed his work, the light of plate tectonics was dawning. Buddenhagen knew that conventional mechanisms were insufficient to explain the jumbled formations he had mapped so well. But 1960s' science was illiterate in the language of this new order. Words and map symbols for subduction zone, mélange, and exotic terrane did not exist in geologic lexicons.

Harold Buddenhagen's suspicion was correct. Today, we know this landscape as the Grindstone terrane, a geologic collage assembled by submarine landslides that occurred more than 200 million years ago on the brink of a subduction zone. The Grindstone's more modern biography was unraveled in the 1980s by two paleontologists and a stratigrapher — Merland Nestel, Charles Blome, and Emile Pessagno — all conversant in the new dialect of moving plates and the chaos of subduction zones.

The notion of plate tectonics, that continents shift— separating, rotating, and reconnecting like participants in a slow-motion square dance — has intrigued people for centuries. In 1838, the Scottish philosopher Thomas Dick first proposed that the continents had moved. Dick noticed how neatly Africa and South America seemed to fit together and in a book titled Celestial Scenery, or, the Wonders of the Planetary System Displayed, he wrote that is was "not altogether improbable that these continents were originally conjoined, and that, at some former physical revolution or catastrophe, they may have been rent asunder by some tremendous power ... " Unfortunately, Dick lacked proof beyond what seems obvious from continental outlines on any world map. And proof, or an understanding of how things work, is essential to science. Without understanding the mechanism, the how of things, science (like the rest of us) simply does not change.

In 1915, a German meteorologist, Alfred Wegener, again proposed that the continents had moved. His evidence was more compelling. He cited the similarity of rock formations in Africa and South America, and Europe and North America, as stronger justification than mere geographic outline. But Wegener lacked a mechanism, and like Thomas Dick's suggestion, his ideas languished as well. Not until technology allowed us to map the seafloor, read the subtle magnetic fields of ocean bottoms, and measure deep earthquakes along continental margins did the mechanism become obvious. The seafloor spreads apart at the mid-oceanic ridge, pushing continents before it or diving back into the mantle in subduction zones, abandoning scraps of seafloor and errant islands at the continental edge like mud scraped off shoes on a front-porch doormat.

In the early 1900s, a remarkable Oregon geologist named Thomas Condon, a contemporary of Wegener, may have recognized intuitively that the oldest rocks of Oregon are immigrants, rocks that originated somewhere else, non-native scraps of crust that had become naturalized citizens by virtue of long residence. In his landmark 1902 book, The Two Islands, Condon wrote, "The geological history of the Pacific Coast consists chiefly in the description of the slow elevation of successive belts of the bed of the ocean into dry land, and the progressive additions of these to the western border of North America."

Condon was ahead of his time. He, like most other scientists of his day, had no inkling of plate tectonics, of moving seafloor and colliding continents. To suggest that the oldest rocks of Oregon had been added to the continent was not only heresy, it was simply a hypothesis without a provable mechanism. And therefore, it was unsound science. So in 1902, Condon's explanation for these exotic rocks was simply that they rose from the seafloor and in the process were heated and deformed. But in his language, "the progressive additions of these to the western border of North America," there is the specter of a deeper and insightful understanding of what we now recognize as truth.

Indeed, the title of Condon's work, The Two Islands, referred to the two widely separated locations of Oregon's oldest rocks: the Klamath Mountains tucked into the remote southwestern corner of the state and the Blue Mountains of northeastern Oregon. Both areas began their lives as volcanic archipelagoes. Both harbor geologic formations about 400 million years in age. Rocks in the Klamaths, if you count the tangled landscapes of the Siskiyou Mountains, and the Marble Mountains and Trinity Alps across the border in northern California, sequester rocks of Silurian and possibly Cambrian age: seafloor perhaps more than 500 million years old. At least one of these Silurian gabbro intrusions, note Rodney Metcalf and Wendy Barrow of the University of Nevada, Las Vegas, include older, Precambrian zircon — a mineral that suggests the gabbro was melted from rocks of an ancient and unknown Precambrian continental fragment.

There is a specific geologic name for a group of rocks that formed in one place and were tacked onto another by plate tectonics. These immigrant landscapes are called terranes, or sometimes, if the rocks have traveled great distances, exotic terranes, a play on the more familiar word terrain. Terranes are fragments of ancient landscapes that have been moved about like plate tectonic chess pieces. Their rocks formed at one location; today they are somewhere else. A terrane is not the landscape before our eyes, but one that requires a deeper vision; it is a geologic landscape. The original mountains, lakes, and rivers are long gone. But their record in the rocks remains. The Aleutian Islands will one day collide with mainland Alaska and Russia and, like a bug on the continental windshield, become a new North American geologic terrane. The Hawaiian Islands are well on their way to becoming a terrane as their extinct volcanoes are carried toward Russia on the back of the Pacific plate. One day, 100 million years in the future, when Hawaii is scraped off the Pacific plate and added to Russia, its rocks will be deformed. Its flora and fauna will be fossils. It will be part of Asia, but its rocks will be recognizable as a former seamount by their chemical composition and mineralogy. The fossils will indicate that the Hawaiian volcanoes once erupted in a tropical climate. And so the history, age, and origin of the Hawaiian terrane will be deduced by future geologists.

In the moving panoply of plates, oceans have opened and closed, continents have separated and melded together in different configurations, just as Thomas Dick speculated nearly two centuries ago. Antarctica has flirted with the tropics, the Amazon with the poles. But even from our sophisticated perspective, we are a bit unsure of the world's precise configuration in the Devonian, 400 million years ago when the rocks of Oregon began.