More or Less Sudden Mountains

Tom Deméré reads the Rose Canyon Fault, the Elsinore Fault, Julian Schist, Friars Road, Mission Gorge, Fossil Canyon.

In ten minutes of walking through Ocotillo's Fossil Canyon, we found dozens of fossils and boulders of limestones, sandstones, marbles, schist, gneiss, quartz, phyllite, and gypsum.
  • In ten minutes of walking through Ocotillo's Fossil Canyon, we found dozens of fossils and boulders of limestones, sandstones, marbles, schist, gneiss, quartz, phyllite, and gypsum.
  • Image by Joe Klein

Rocks are for climbing, collecting, throwing, building. They're also full of information, if you can read a rock. Scientists who become fluent in rock — geologists — peruse these old, hard texts and interpret them. Rocks chronicle what lived and when, how long things've been around, what it all looked like millions of years ago, what creation is made of, how we got to be where we are: rocks are magnificent writers. The rocks in and around San Diego have composed amazing, fiery stories for a very long time. An ancient ocean once covered this county; volcanoes used to spew here; and more or less sudden mountains rose and fell in San Diego more than once.

We stopped once along the 8, near Alpine, and Deméré bent down by the side of the road. "This is where our beaches come from."

We stopped once along the 8, near Alpine, and Deméré bent down by the side of the road. "This is where our beaches come from."

This area is currently the most geologically active and diverse in the country. Our rocks are still writing away, every single day. Which makes these rocks of San Diego a good substratum for human writers as well. When specialists write or talk about rocks, they use weird words like gneiss, schist, plutonic, igneous, and zeolite. They could be carrying on about lizards or gods or cacti for all most of us know.

Tom Deméré: "I used to surf a lot. On bad surf days, I'd check out the terrific exposure on the sea cliffs."

Tom Deméré: "I used to surf a lot. On bad surf days, I'd check out the terrific exposure on the sea cliffs."

Personally, I have trouble with the words that specialists use to refer to rocks; but since I'm writing an article about rocks, I'll have to work to keep the information tight and together. The earth, in essence, is one big rock. Talk about heavy subject matter. Our mother rock's so massive she's on fire in her center, molten from her own intense pressure. This is a potential that exists inside every rock.

Deméré wanted to show me "samples of some of the oldest rock in the county." It's called Julian Schist. Geologists estimate the stuff to be as much as 400 million years old. Along Route 78, up Banner Grade, at an elusive spot, Deméré found what he was looking for.

Deméré wanted to show me "samples of some of the oldest rock in the county." It's called Julian Schist. Geologists estimate the stuff to be as much as 400 million years old. Along Route 78, up Banner Grade, at an elusive spot, Deméré found what he was looking for.

What I really need, to help in the translation of so much colossal material, and ultimately to pore back over the ancient natural history of San Diego County, is an honest-to-goodness, real-life geologist.

In San Diego, we've got lots of geologists. Most of the ones here work for the geology department at San Diego State University. The program at State's been around for over 70 years. Today, their laboratories boast cutting-edge facilities like ion chromatographs, mag separators, gravity tables, and jaw crushers. Their website shows composites, bios, and e-mail contacts for over 25 highly trained, advanced-degree-holding geologists. Surely, if anyone ever required rock-related aid, then San Diego State'd be the locale to go to.

I want to mention, as an aside, from the pictures on the SDSU website, that geologists don't particularly look like geologists. Not that I can tell you exactly what I think a geologist is supposed to look like. It's just that geologists don't seem to share a single discernible physical "type." That is, each one of them looks more or less completely different. I don't know why this would surprise me — the fact that geologists can be jolly and dour, young and old, men and women, long-haired and short-, from here and from elsewhere — except that I thought a life with rocks would, I don't know, kind of turn a person into stone a little, maybe harden an individual's demeanor, the way old married couples finally tend to look alike. Geologists do share some similarities, of course. For one thing, they appear reluctant to respond to mass e-mails from the media. Within the body of the personal-ad-like e-letter I sent them and sent them and sent them, I wrote that I would need "access to an articulate and engaging geologist, for interviews and a long drive or two on a network of roads." Then I went on to indicate that I would want the geologist "to comment on what he or she sees as we drive and to stop me when we see something interesting, to get out of the car, hammer on rocks, describe them, and explain exactly what these rocks tell us re SD paleohistory."

I received exactly two responses. One geologist sent back word that he was "looking into it." And the other provided me with a nomination. David Kimbrough e-mailed back that I should be talking to the folks at the San Diego Natural History Museum. "Tom Deméré is the person to start with," Kimbrough wrote to me. And so I sent a copy of my eager mass electronic mailing to this man at the museum, this recommended geologist.

Tom Deméré, Ph.D., replied immediately. Only he didn't just e-mail, he called me. And his reaction was enthusiastic. When we talked about a driving trip, he said, "It sounds exciting."

Exciting? Why not, I thought. Our San Diego County landscape has made me want to pull over and break into spontaneous applause now and again. And if this Deméré fellow could find it "exciting" to drive and look at rocks all over creation for the better part of a hot April day, then he was definitely my Rock Man.

Our region has a natural history that extends back millions of years and encompasses many past physical "stages" and biological "players." Even the slightest glimpse into this dynamic past leaves me with a profound sense of wonder. That's a quote from Deméré, the quote he chose for his page that links to the San Diego State University Geology Department's website. The university lists Deméré as an adjunct professor, which means that SDSU doesn't pay him but it does extend to him unlimited lifetime access to its facilities, collections, and libraries.

As curator of paleontology, Dr. Deméré has occupied the Joshua L. Bailey Jr. Chair of Paleontology at the Museum since 1994. (Now I'm reading from the San Diego Natural History Museum's website.) Before that he served as collection manager in the department. Tom's research focuses on the evolutionary history and paleobiology of pinnipeds and cetaceans. ("Pinniped" and "cetacean" are the scientific words for seal and sea lion, porpoise and whale.) [Deméré] is also keenly interested in the geology and paleontology of southern California and Baja California and has published numerous scientific and popular articles on these subjects.

Deméré's credentials were impeccable, and he was into the idea, so we scheduled a real-life rock-reading field trip. We would meet at 8:00 a.m. in Balboa Park, in the parking lot of the museum, and then head out to study the roadside rocks of San Diego County.

As a kid, I always loved field trips. They were like days off from school, but you still got credit for going. And when I look back at my life's field trips, I realize they always managed to teach me something, no matter how much I goofed off.

That said, the prospect of my first official rock-reading field trip did daunt me a bit. To drive into the desert and pick over stones, what does one need? What do first-time geologists wear? Should I pack a lunch? Would I be overburdened, or underprepared?

The morning of our trip, Deméré emerged from the museum decked out in flannel and denim. He was all good mornings and smiles. Lean and wiry, Deméré appeared at once distinguished and tough, a curious combination. He has a quiet, stately air underlying what I took to be concentrated intensity, very much like the museum in which he works.

Deméré packed boots, sunglasses, binoculars, a camera, rope, lunch, and the defining tool of his trade: a pick. A pick is a dangerous-looking weapon. Deméré's pick weighs about seven pounds; it's three feet long. And not only does he chip away rock with it, but he uses it as a walking stick and also a comfortable seat in the field. A few hours into our trip, Deméré also produced a hat exactly like the hat of Indiana Jones. He grimaced at the association, but it tied together my impression of Dr. Tom Deméré.

Before we could leave the parking lot, Deméré wanted to show me around his workplace. We went in one of the back doors of the Natural History Museum, up some metal staircases, and entered the offices and private collections area somewhere far away from the main exhibits. Deméré had laid out maps across a broad table: he wanted to give me a sense of what we would be seeing that day.

Deméré illustrated how San Diego County is divided into three distinct geomorphic sections: the Coastal Plain region, the Peninsular Ranges, and the Salton Trough. He pointed out numerous fault lines that riddle our city and the areas around it. He started to tell me about the landscape and about the kinds of rocks inside the landscape, and then, as he tried to wrestle his giant maps back into tidy rectangles (note: geologists don't seem to be any better at map folding than the rest of us), Deméré explained that we would have to "look through the topography and try to see the geology." This interesting theme would resurface often over the course of our trip.

After the overview, we took in a short tour of the museum's impressive fossil exhibits. You should go to the museum yourself to see them; they're fascinating and informative. And, unlike in any natural history museum anywhere else that I've ever been, the fossils in San Diego's museum are local.

During the museum tour, Deméré tried to engage me in all sorts of technical rock-related conversation. But I could hardly keep pace. We hadn't even seen a single wild rock yet, and already my head was juggling more new phrases and concepts than I could comprehend.

One thing I started to think about, as Deméré and I piled into my car, was the concept of time. In Real Time, it was 8:27 a.m., the 22nd of April, 21 minutes since we'd met, etc. But the thing I know about Real Time is that it isn't real at all; it's just a useful, simple, invented, human concept. This thought, combined with what I'd heard Deméré expound about epochs and eras, got me to considering other philosophical notions of time. Specifically, I started to contemplate the kinds of time that our respective jobs (writing and geology) represented to my rocking mind.

In Writing Time, we are roughly 1659 words into this article. It has probably taken you somewhere between 6 and 11 minutes of Real Time to read your way here. (Unless you're like me, and you prefer to go through written works in more than one sitting, in which case it may have taken you many days to read this.) Regardless, it took me several weeks of Real Time to write my way here.

But true Literary Time has less to do with reading and writing than it does with the time of the human imagination. This is to say that Literary Time is, in the end, largely a product of a writer's style. For example, I may alternately choose to embellish or leave out whole portions of our trip. One writer's moment may linger pages on a single description, while another's digresses sentence by sentence over multiple ideas and events.

But Geologic Time... Geologic Time is Real Time taken to stupendous limits. I find the only way to understand the scale of Geologic Time is to employ an analogy. Think about it like this: human beings live, on average, 75 years of Real Time. The average rock has been around for somewhere between 4 million and 400 million Real Years, depending on the rock. That means a single second in Geologic Time lasts more Real Years than a person lives. Start now. Now. Now. How much can you do in a single second? One Mississippi. One one-thousand. What can you say or get done? Well, that's how much the average rock does while we're toddling in diapers, learning to brush our teeth, finishing school, conquering adulthood difficulties, raising families, and aging gracefully. No wonder rocks don't seem to accomplish much of anything.

Such has been the gist of my musing, which, in this article's convoluted version of Literary Time, brings my writing and your reading neatly back to the beginning, to the Real Time commencement of our geological field trip.

Tom Deméré and I piled into my beat-up old Ford Explorer. The plan was to drive around locally for a bit, in the canyons around the museum, and then to head out through Mission Valley, up into Mission Trails Regional Park, and then to take the 8 to Ocotillo, exit into the Coyote Mountains, and finally loop back through Anza-Borrego, Shelter Valley, and Julian, and come home.

As we started out, Deméré spoke about being careful not to be "distracted by the landscape." He used delicious expressions like "botanical overburden." He lamented the covering presence of asphalt and lawns and houses. Deméré also spoke of rocks as being "tenacious," and he seemed pleased to note that for all the botany and landscaping and housing, eventually the rocks would prevail. At one point we noticed a plant ("green-finger dudleya," I observed) growing through cracks in some rocks ("plutonic igneous," said Deméré) beside the road. Deméré made a defiant noise in his throat, "Hah!" And then told me, "The rock's winning!"

We were setting out to read rocks, and Deméré was showing me the best places to read through the most rocks: "road cuts." In fact, it seems the majority of modern geology and paleontology (the study of fossils) is done in construction sites and road cuts. These are the locations where geologists and paleontologists can find the largest samples of fresh rock.

Modern contractors and their massive yellow machines slice indiscriminately through broad swatches of earth, and no little rocks, no softer units, are allowed to hide. Without the samples of fresh rock that these major undertakings provide, all geologists and paleontologists could do is drill a hole or find natural stream cuts, which are few and far between. Modern geologists are fortunate to live in a time of road building and expansive construction.

But, sadly, road-cut geology isn't as reliable a source of information as it once was because the newer road cuts are landscaped as fast as they're made. The reason for the hasty reshaping is fear of erosion. At one point, Deméré told me, "Quote me on this: 'Our recent obsessional fear with erosion is threatening road-cut geology with extinction.' " The problem is that, for the past 15 or 20 years, road cuts have been quickly covered with flowers, grass, and trees. One of Deméré's loudest laments centers on hydroseeding. I'd seen the stuff before, but I'd never heard the term "hydroseeding" until Deméré employed it.

According to one website, hydroseeding "looks like fuzzy green paint along the side of a road or surrounding a new building. Hydroseed machines mix together seed, water, fertilizer, tackifier (glue), and green wood fiber mulch to create a slurry. The slurry is sprayed on the ground with a high-pressure hose which helps it to reach all kinds of terrain, like slopes, that may be difficult to reach. When the slurry dries, it creates a crust over the ground, protecting the area from erosion. The crust protects the seeds from being washed away in the rain or eaten by birds." This green gluey crust also renders any rock in the area unreadable.

Looking at the first of many instances of San Diego hydroseeding, across from Costco and Ikea along Friars Road, Deméré declared, "I don't mean to dis botany completely. I can appreciate plants." But more often along our trip he would indicate that roadside landscaping was, to a geologist, a kind of proliferating evil.

Friars Road scores an interesting geological swath. The core rock along the canyonsides is called Friars Formation. And the distinctive combination of overlying cobbles and pebbles and boulders is labeled Stadium Conglomerate. These rock units were designated officially in 1971. Geologists will name certain stone combos for the places where they're first found, which is to say that someday someone might come across a cliff of Friars Formation or Stadium Conglomerate in Antarctica. You never know. Deméré pointed out that strata of the Friars Formation (mostly gray sandstone with some green claystone layers in it) had been exposed and was quickly being covered, by the construction sites along Friars Road.

There's a rock quarry off Friars, at the end of Qualcomm Way, where they mine Stadium Conglomerate. It's one of just a few quarries in San Diego. At the quarry in Mission Valley, they're digging up stones brought into this area by an ancient river that essentially made a huge cobble delta 38 to 50 million years ago. Now the remnants of that delta are being used as aggregate in roadbeds and asphalt.

Eventually, Friars Road merges with Mission Gorge Road, which winds its way up through some magnificent escarpments, until finally you can turn off into Mission Trails Regional Park. Here, the San Diego River Valley narrows due to the hardness of the rocks. On the east, dark red to black volcanic rock rises majestically, and on the west slant of the valley, light-colored plutonic igneous rock slopes and looms. This plutonic stuff is riddled by lines: faults and joints.

To describe how this rock formed, Deméré used the metaphor of an ice tray. "You know how there are these compartments in an ice tray between the individual cubes. Well, the pressures exerted on this rock from all sides have shattered it vertically and horizontally until you get this patchwork pattern of divided blocks of plutonic igneous rock." To me, the stuff looked like it had been piled there, huge heaps. But that's not it at all. Deméré explained that this rock had formed far beneath the surface of the earth, where the cracking took place, and only recently had the rocks become exposed above ground. "The joint planes are caused by a release of pressure during a long period of crustal uplift and erosion. We call this action 'unroofing of the batholith.' That whole formation there was once a solid mass of granitic rock." He was pointing at a natural hilltop sculpture of perhaps a hundred different stones.

Somewhere in Mission Trails -- a low red cliff uprising close by on the right and a brushy hillside falling gently to a valley on the left -- we got out of the car. Deméré pointed to the red cliff and what he called "the toe of these slopes," and he said, "that apron of debris... See it? That's called 'talus.' Talus is like this chaotic accumulation of angular assorted stones. It's what a landslide looks like inside."

Deméré has these imaginative ways to describe how rocks look and how they formed. He talked often about the history of various rocks. "With this rock here," he said, pointing to yet some more plutonic igneous formations, "you can imagine that we're standing ten kilometers underground, swimming in magma. And then it all begins to cool slowly into crystals." Then he said, "Think of a Lava Lamp. Plutons, or spumes of less dense molten material, rise through material of higher density. We call this action 'pluton implacement.' "

As we drove farther, onto I-8, and started to head out into the heat, Deméré spoke dreamily about plate tectonics and how rock forms in and around these giant shifting pieces of earth. "Plate tectonics is to geology what the general theory of relativity is to physics: it's a unifying theory for the earth sciences. Basically, it's proposing that the earth's surface is divided up into a series of plates. The use of the term 'plates' gives us a sense of the large lateral extent of these formations relative to their thickness."

He went on. "These crustal plates -- the crust is the surface of the earth -- are mobile. They're moving around relative to one another so that they contact each other on three different kinds of boundaries. Along a collision boundary, which also has another name, 'subduction,' the plates crash into each other, and in some cases one slides beneath the other, which is what's going on along the northwest coast of North America. Sometimes when plates collide, they create mountains, like the Himalayas. But when one of the plates slides under the other one, that's subduction, and the subducting plate begins to melt. That's when you get plutons and volcanoes." (That's also when crustal uplift and erosion can cause batholiths to get unroofed, by the way.)

"Plates also slide past one another," Deméré continued. "And that's a transform boundary. The San Andreas Fault is an example of that, although most such boundaries occur on the ocean floor. And plates also spread and move away from one another, and that's where new crust is being generated, typically in the mid-Atlantic and the mid-Pacific, and those are called 'spreading boundaries.'

"Plate tectonics explains why volcanoes are where they are and why earthquakes occur where they do."

As Deméré talked, I started to imagine geologic events -- big ones like earthquakes and rock slides, yes, but also small ones like river-lifted pebbles or windblown sands or Geoff-thrown stones -- as being breathless celebrations, incredible expenditures of energy in the "life" of a simple rock. It occurred to me that a rock is never so discontented as to rush around under its own animation. Rocks are patient enough to wait for what moves them.

We stopped once along the 8, near Alpine, halfway up an extended steady climb, all green hills and sun, and Deméré bent down by the side of the road. "This is where our beaches come from," he said, sifting tiny particles through his hands. "Hard rock, exposed at the surface, disintegrates out here and produces these particles of decomposing granite. Then it washes down dozens and dozens of miles to the sea."

Later, looking around at the whitish mountains near Ocotillo, Deméré told me a little of his own history. "My first experiences with geology came from my interest in surfing," he said. "I used to surf a lot. On bad surf days, I'd check out the terrific exposure on the sea cliffs." Then he added, "Actually, I got interested in geology when I started looking around at the hills out here and realized there was a history there, that we're all part of an incredibly long history. Some people say that this makes them feel insignificant, but for me it makes me feel a part of something, like I'm part of some bigger significance."

As the miles fell behind us, I asked Deméré to distill geology down into an idiot course for me. Here are a few paragraphs paraphrasing what he said.

By definition, a rock is a solid inorganic mass or compound consisting of an aggregation of at least two minerals (although there are some exceptions, when a rock may consist entirely of one mineral). To classify a rock, three things must be considered: (1) origin, (2) composition, and (3) texture. The first step to identify a rock is to try to categorize the rock into one of the three main types, or groups, of rocks. These include igneous, sedimentary, and metamorphic types. The only rocks that do not fall into one of these categories are meteorites. Igneous, sedimentary, and metamorphic rock types are distinguished by the processes that form them. Igneous rocks form by crystallization from magma. Crystallization can occur at significant depths below the earth's surface (forming plutonic igneous rocks) or at or near the earth's surface (making the rocks volcanic igneous).

Sedimentary rocks form by the accumulation of small or large grains or fragments of preexisting rocks (like sandstone) or by the precipitation of mineral matter from a body of water, such as an ocean, lake, or stream (like limestone).

And metamorphic rocks form from preexisting igneous, sedimentary, or metamorphic rocks. Heat and/or pressure and/or migrating fluids cause the original mineral assemblage of the rock to change to a new assemblage of minerals.

Some rocks exposed at the surface are young, but most are very old. In fact, most rocks are much older than the historical records of man. These "old" rocks are generally many millions of years in age. Units of geologic time include the "era" (longest), "period," and "epoch" (shortest). All of geologic time (about 4.5 billion years) has been divided into four main eras, called (from oldest to youngest) the Precambrian, the Paleozoic, the Mesozoic, and the Cenozoic.

The earth has slowly changed throughout its history and continues to do so. As a result, certain time periods during the earth's history had conditions more conducive to formation of specific types of mineral deposits.

One hundred miles outside of downtown San Diego, our heads practically coagulating with rock lingo, we arrived in Ocotillo, near the Coyote Mountains. Out there, the sun's roasted the whole area to one whitish-yellow, sandy expanse. Even the trees, such as they are, share this wan color. Apparently, geologists go out to Ocotillo often. The limited plant cover makes this a valuable place for geologists. They call the most geologically fruitful part of the mountains there Fossil Canyon.

After a stop for snacks and water, in 90-degree heat, we off-roaded past the Lazy Lizard saloon into an area Deméré described as "a puzzle thrown into a box." He pointed out fault lines running the length of the mountains, explaining how sedimentary, metamorphic, and igneous rocks are all present there, butted up against each other. "We come out here to repiece the puzzle," he said, pick in hand.

In ten minutes of walking through the hotness of Fossil Canyon, we found dozens of fossils (mostly shells of clams and snails), as well as boulders of various limestones, sandstones, marbles, schist, gneiss, quartz, phyllite, and gypsum, all just lying around in haphazard arrangements that Deméré dubbed "hummocks." He used his pick to dislodge a fossil or two (he has a special permit that allows him to remove what he finds there) and gently quizzed me about rock types. I did my best to guess and pay attention. Gypsum kind of glows a little, like satin. The surface of gneiss (pronounced nice) is usually riddled with alternating lines and patterns. And phyllite appears distinctly wavy.

As we headed out of Fossil Canyon, driving along the line of the Elsinore Fault, Deméré summarized the crisscrossing paths of fault lines that slowly and surely draw the land mass of our county every which way.

"Onshore, we have two primary fault zones in the city of San Diego," he said. "The Rose Canyon Fault Zone comes onshore at La Jolla Beach and Tennis Club and then swings around the east side of Mount Soledad, which has been uplifted along the fault, and then down Rose Canyon and along the east side of Mission Bay, along I-5, and then underneath the whole downtown area. To the east of that is the La Nacion Fault Zone, which runs parallel roughly to 54th Street, all the way down to Otay Mesa.

"Extending east, we have the Elsinore Fault, that runs roughly north-northwest, and farther east we have the San Jacinto Fault, which runs roughly parallel to the Elsinore Fault. And then farther east still is, of course, the San Andreas Fault, out beyond the Salton Sea in Imperial County."

When he mentioned the Elsinore Fault, Deméré pointed out the window, across the sandy fields of Anza-Borrego, to the gray mountains in the distance, and he said, "You can just about see the line of the Elsinore Fault right there. You can see how the two sides of it are different, where the two crustal blocks are moving slowly past each other." I think I knew what he was pointing to, but then, I couldn't be sure. It's like when my amateur astronomer friends would show me certain lesser-known constellations: in the end, I could nod, yes, that I could see the swan's neck or the hero's sword, but all I was sure I was seeing was a suggestive gathering of stars.

For our last stop, before home, Deméré wanted to show me "samples of some of the oldest rock in the county." It's called Julian Schist, and it's continental material that has been metamorphosed. Deméré told me that this ancient sedimentary rock existed before just about any other solid thing. He said that geologists estimate the stuff to be perhaps as much as 400 million years old.

Along Route 78, up Banner Grade, at an elusive, almost nondescript (to me) spot, Deméré found what he was looking for. As a deer dashed off into the trees to our right, Deméré made us stop to see the Julian Schist that had shed its mantle of plants. Schist is pretty weathered stuff: very brittle, breakable by hand. And according to Deméré, we do know how schist happens: this rock was part of preexisting "roof pendants," hanging over the magma chambers deep inside the earth. Eventually, the magma intruded into this country rock, recrystallizing old shales and mudstones with intense heat and pressure. And near Julian, some outcroppings of the old schist remain in view.

It was lunchtime. Our field trip had brought us here, up the back side of the Peninsular Ranges, at an outcropping of ancient rock by the side of the road, and Deméré was explaining the big picture, telling me how San Diego County came to look the way it does.

"Going back in time," he said, "we see different plate boundaries here in western North America. During the Jurassic, we had a subduction plate boundary, when the rocks formed in Spring Valley and on Black Mountain. Black Mountain, Dictionary Hill, San Miguel Mountain, and the San Ysidro Mountains are remnants of a series of volcanic islands that occurred in this region 140 million years ago. They were fed by the melting edge of a subducting plate. A modern analog would be the Japanese islands. So it appears that, 140 million years ago, we had a geography that looked more like Japan than California.

"Then, 100 million years ago, subduction continued, but we had stopped at a continental margin that looked more like the coast of western South America. So we had more of an Andean-style geography, just as an analog. Big mountains right on the shore. It appears that the sea between our Japanese-style volcanic islands and the North American mainland to the east ended up telescoping on itself because of the plate boundary where the plates were colliding. So the margins between these plates just essentially swallowed up that inland sea and sutured the volcanic-island arc to the mainland of North America. "Then we had a period of major erosion, which essentially flattened these Andean-style mountains. This period of erosion lasted for perhaps 30 million years. And by that point we were exposing the roots of these mountains. Essentially, erosion stripped off the mountaintops. So by that point, 50 million years ago, we had a geography that was more like the Texas coast, with large rivers moving across the land and bringing all those cobbles and pebbles and boulders that we mine in Mission Valley.

"Next, we had long periods of lowered sea level, when Antarctica began to experience glaciation, about 30 million years ago, coupled with all the erosion, and so we don't really have a local record of what happened then. We have what's called an 'unconformity,' a gap in our geologic record. For the most part, we have a big gap in the record from about 30 million years ago until about 5 million years ago. There were just long periods of erosion or nondeposition, where the rocks were either stripped away or they never accumulated.

"In the last 5 million years, the modern transform boundary has begun to form, with plates sliding past each other, and the Gulf of California has opened up, with the Baja Peninsula tearing away from the mainland of Mexico and bringing us along with it. Our Peninsular Ranges have probably only been uplifted within the last million years. That's somewhat controversial, but what little evidence we have seems to point in that direction.

"And finally, in the past 2 million years, the world has been enduring dramatic geological changes correlated to periods of global warming and global cooling and related periods of rising and falling sea levels."

Deméré was chatting dreamily, laying it all out, making the vast pathway of natural history seem humanly passable, perfectly negotiable.

And as we took our lunches there, by the side of State Route 78, up Banner Grade, with the earth changing slowly beneath us and Deméré talking and sitting half-comfortably on the jagged ancient schist and me leaning there scribbling these hasty notes, feeling somehow unified with these slow events and my newly expounded surroundings, I realized: it's only just a matter of time.

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