Driving The Sonoran Desert

Sonoran Desert

I’ve heard many people remark that driving the desert is boring. To me, the main highlight of a drive to or from Phoenix is the Sonoran Desert.

This vast area of sand was once a shallow inland sea. It’s essentially flat, with little islands of rock and rubble poking through here and there. Or, so it’s easy to imagine, driving the desert between Phoenix and the Colorado River.

Fossil evidence for marine habitats dates back to algae colonies about 1.2 billion years ago. More recently: sharks, corals, trilobites, clams and oysters, and those monster sea-going dinosaurs. More recently than that: traditional dinosaurs, duck-billed and otherwise. Even the most obvious visible features of the desert have been around for a very long time.

According to one geological site I once researched, one particular black dome, a few miles north of I-10, could be over one billion years old. The main mountain range to the north looks like a line of weathered peaks buried up to their necks in sand and scree. They are mostly buried in their own debris. The oldest rocks date to about 1.4 billion years.

These mountains don’t appear to be much by Sierra or Rockies standards. For one thing, they’re much older, and they look it. Elevated topography here is mostly crumpling ancient volcanoes, with a few low, eroded mesa plateaus thrown in for effect. The desert floor from which they protrude brings us to the second thing. Like the volcanic islands of Hawaii that rise through 20,000 feet of ocean before breaking the water’s surface, there’s no telling where the bases of these more modest rounded brown Sonoran things really rest.

The Colorado carved out the Grand Canyon about 17 million years ago. To fill Sonoran basins, the forces of wind, erosion and exfoliation have enjoyed over a leisurely billion years to level the playing field. Protruding objects may be deeper than they appear.

In some areas near the Colorado River border with California, the roadbed is cut from the sides of lava deposits hundreds of feet thick. You don’t have to have a trained eye to spot it. It’s not subtle. For a few bucks you can get a cubic yard of the familiar landscaper’s lava rock from Orchard Supply or Home Depot. Would you recognize a cubic mile of the coarser grades of the same stuff?

These deposits are from a period of intense volcanism 25 million years ago. While that’s indisputably old, and the age easily explains the drastic erosion of most of the prominent geological features, one senses – and how could one have guessed before modern dating technology? – some of this is much older.

If driving east, we see a vast horizontal sandy white line that arcs like the rim of a bowl from roughly northeast to southeast. We can say the line is “level” because it could have been laid out with a transit line. To my eye, there’s no other explanation for it. If that isn’t a beach line, I don’t know what is. A beach, that is to say, “beached” high and dry some hundreds of yards above our heads.

Imagine overhead then, one of those archaic 40 foot sea monsters, plesiosaur – a dinosaur with flippers – cruising on the prowl for an ancestor of the Great White, perhaps, as a late afternoon snack.

In the same part of the Sonora (near Quartzite) we find an attraction called “Dome Rock”. Somewhat reminiscent of a shark fin, a perfect parabolic bell curve rises hundreds of feet above the desert floor. It’s a volcanic mound. Sadly, it is girdled by a spiraling road cut up to the top. Even in the desert, there’s not much that hasn’t been explored and spoiled by jeep, ATV or dirt bike.

There are several other unnamed volcanic mounds, a few hundred feet high only, of which just the dark brown lava plugs remain intact. These too are mostly buried in their own rubble, consisting of what once was the volcanic cone that contained them.

There’s a remarkable profusion of plant life out here. Desert photographs come out “too green”, even in August, because there’s a richness of green vegetation.

Where there’s plants, animals and insects are sure to find a niche too. Speeding through the desert at 75, you won’t see much animal life, but you’ll see the saguaro everywhere, the iconic cactus native to the Sonoran. Oddly, approaching the Colorado driving eastward on the California Mojave side of I-10, you won’t see a single one. As you cross the border inspection station and bridge, you’ll start to see a profusion of the famed “one armed bandit” saguaros, beginning within a hundred yards or so.

At first inspection, the Mojave generally comes across as a poor cousin to the Sonoran. The visual differences on the other side of the Colorado are so striking and identifiable that, if you awoke from a nap as a passenger in the car, you could look out the window and instantly see which desert we were passing through. The Mojave usually is and looks bone-dry, and is sparsely vegetated with low scrub. The brightness makes on want to squint. There is so little rainfall along the Mojave I-10 that a measure of a “failed town” is the number of its dead palm trees. In the vicinity of Twentynine Palms (CA) one sees unfinished roadside developments with the sagging carcasses of hundreds of palms. I did not know before that palms can wilt, like gargantuan dead brown asparagus spears.

I have camped in the High Mojave in the past. It has secrets of its own, including the beauty of pristine and austere severity, and absolute silence. Outside the boundaries of the human encampment, sounds are so few and far between that any sound at all is a distinct event, and you have all the time in the world to savor and analyze it.

Unlike the Sonoran, the Mojave gets little or no benefit from the North American Southwest’s July-September “monsoon season”, during which the Gulf region dumps huge masses of warm, moist air as far west, it appears, as the Colorado. The resulting thunderstorms are unpredictable, but can be both awesome and torrential, when you can get them. Monsoon season usually accounts for the bulk of Arizona’s annual rainfall.

In some years, most of that can come from one single storm …

Flash floods quickly result from periods of intense monsoon activity. One year, the back yard of the Phoenix house began to flood, threatening the pool and the house itself; I dug an emergency drainage channel to the street frontage; all I had to do is shovel out an elevated dirt area, and the muddy standing water cut its own trench to the storm sewers.

In that same year, some brave but foolhardy soul, ignoring permanently posted “do not enter when flooded” warning signs, tried to ford a flooded underpass in a jacked-up 4×4 pickup. The water was actually about 8-10 feet deep, and he drowned.

For all the talk of desert heat, it’s often hotter in town. On my August drive, outside air temperature is about 107F, the car thermometer says. That’s still about 6 degrees cooler than forecast for downtown Phoenix.

The desert can dump its heat at night, radiating it into the night sky. The city can no longer do this. It’s trapped in a heat cocoon of its own making. Heat absorbed during the day, stored up in all that urban blacktop, re-warms the night air faster than heat radiation can cool things back down. Night-time temps rarely get below 96 in the coolest, darkest period of the city summer night.

Contrast that with “Man vs. Wild” stories of unprepared hikers and stranded motorists who die of exposure in the desert night.

I have loved the desert for many decades, but it is true that I love the mountains too, and probably more so. My hiking years were all spent in the Sierras, from Tahoe National Forest down to Kings Canyon. Still, any time you wanted to see where you’d been, or what was in store for you on the trail ahead, you usually had to climb a prominent landmark for a view, or wait until punished by your next mountain pass. Environmentally speaking, as you hike the mountains from localized niche to localized niche, you use a trail map or a 10,000 foot pass to connect the dots.

After our discussion of fossils, geologic eras and rainfall statistics, it sounds ever so lame and weak to state that the desert “seems old”. But we’re not talking “years”, we’re talking geological periods or epochs. We measure time not in years, but in “Ma” and “Ga” – millions or billions of years ago.

Given that young Earth had no permanent “continental” land masses at all for the first 1.6 billion year of its 4.6 billion year journey through time, desert features and artifacts that go back from 25 million to 1.4 billion years almost shout their complaint about the debilitating effects of advanced aging. It’s not that kind of effect, nor some appearance you can discover or replicate, that we see on that big boulder they trucked into the local downtown park in 1967 or so.

Desert rock isn’t just brown from volcanism. Everything has browned from age, and no doubt, from solar UV rays. You see this patina on the baked stony meteorites that survive the plunge from the solar system’s origins to Earth’s surface. You can see this in parts of Australia and a few other isolated geological islands of time on the globe. Even the sacred granite cathedrals and domes of Yosemite look fresh and young by comparison.

After the land lifted and the water receded, and the volcanoes covered everything with a thick mantle of lava, nature set about wearing down this magnificent young landscape into a rubble pile – the “debris field”, in the parlance used for much quicker destructive events. I created you, but see what I can do to the young and proud.

The desert waited, and waited, and endured.

The Appalachians were born about 480 million years ago. Their rounded slopes and modest elevations show advanced weathering. The mighty Himalayas started their upheaval (forming Mt. Everest) about 70 million years ago. The upstart Sierras formed with its Mt. Whitney, in stages, from 65 to 4 million years ago. Their turn will come too. It is already coming. The timeless desert waits patiently. It will be there when the newcomers falter and crumble.

Though the mills of God grind slowly, yet they grind exceeding small;
Though with patience He stands waiting, with exactness grinds He all.

In the desert, to see where you’re going, look ahead. To see where you’ve been, turn around. If you measure time by changes in locale, there’s no sense of time in the desert. Past and future are both right here, wherever you’re standing, which is the present. Wherever you go, you’re still in the middle of it.

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