San Juan Mountains offer glimpse into ancient geology
SAN JUAN MOUNTAINS, COLO. — About 1.8 billion years ago, volcanic islands bulged out of the ocean off the south coast of what would become North America. They massed in an area humans would eventually call the Four Corners, and ground north, building out the shoreline. Little oceans pooled in their basins, but they contained no fish. Only bacteria lived on Earth when Vestal Peak began to emerge east of Molas Lake.
"Looks vertical from here," Ed Epp said on July 24 looking at a ridge from a meadow below Vestal Peak.
Epp, a geologist, had hiked more than 7 miles with me to the meadow where we were now finishing our dinner and boiling water for the next day. In the morning, we left the parking lot at Molas Lake, which is north of Durango, Colo. The next day, from base camp in the meadow, we hoped to climb the mountain.
But Epp was worried. He spooned reconstituted freeze-dried dinner from a pouch into his mouth as he looked up at the mountain, darkened by rain. Its 1,600-foot north face — Wham Ridge — was our route up, and it would be dangerous if it was wet the day of the climb. The rock is quartzite, which can seem slick even on dry days, and like a slide, the route steepened as our eyes traced up to its clouded 13,864-foot peak. At the top, it did look vertical.
Epp gazed up from camp, chewing.
"No real easy way out of there," he said.
According to Fort Lewis College Professor David Gonzales — a geologist in Durango for more than 20 years who was interviewed after the climb — the surface we were looking at that Friday afternoon was once at the bottom of the little oceans that formed 1.7 billion to 1.65 billion years ago off the coast of what would become North America. It's called the Uncompahgre Formation, he said.
At the formation's base on the day of the climb Epp picked up a rock rippled by ancient waves that had rolled through the long-gone bay. But it would have been a bay without seagulls or sharp grass growing in dunes. And no crabs. No fish. No life as we know it.
"It would have been absolutely silent," Gonzales said. "Except for wind. And waves."
But the landscape changed between 1.65 billion and 1.6 billion years ago. Plates that pressed the volcanic islands into North America were still inching north, and in that time frame, the edge of the continent broke under the pressure.
"The whole marine system got smashed by continental movement, folded and buried," Gonzales said.
Like a slipping rug, it rolled up and onto itself, covering the volcanic land and the little oceans. Those oceans contained silty, shaley sediments and quartz-rich sand. But heat and pressure underground hardened the minerals. Over time, they formed into phyllite and quartzite, lines of which jump through the cliff sides around Vestal Peak like pulses on an electrocardiogram monitor.
Then, after the folding, approximately 1.45 billion years ago, a molten fist of granite thrust through the Uncompahgre Formation. It hardened and created the Needle Mountains. About 5 miles south of Vestal Peak sits Mount Eolus, the tallest mountain in that range at 14,083 feet.
Millennia crept by.
And then another plate buckled under what is now North America, uplifting blocks of the buried formation and burying other parts of it deeper. That happened about 300 million years ago, Gonzales said. He's seen one of the blocks in Ouray, Colo.
Streams and rivers cut into the new mountains, and erosion washed the young earth and softer rock off parts of the formation, bringing it into a new world. Now, there were ferns and fish and other cold-blooded creatures with spines. Soon — in about 70 million years — there would be dinosaurs.
But the Pacific plate had for almost 200 million years been sliding silently under the west coast of the continent, creating heat that spurted more volcanic arcs onto its edges and building more land-locked oceans. Then between 70 million and 50 million years ago, that subduction lifted the continent's edge, buckling the west coast and southwest Colorado.
That created the Rocky Mountains, which contain the San Juan Mountains that encompass Vestal Peak.
"And that brought this whole package of rocks — everything that had been pushed up — to at least 14,000 feet," Gonzales said.
That Friday night in our tent, rain fell intermittently in the meadow. But when I woke at 5 a.m., stars were scattered throughout the sky. I fell back to sleep, hoping in a few hours the sun would burn off all of that night's moisture.
The next morning, the sky was blue. "Wow," Epp said, emerging from the tent.
The trail from the meadow wound up a steep hill through bushes still wet from rain, and then, hundreds of feet above tree line, we walked over a field of boulders that clinked when they shifted under our feet. Epp stopped occasionally to marvel at the landscape.
"Oh, look at the moraine," he said, pointing to a mound of boulders that had been dragged down the cirque between Vestal Peak and the mountain west of it, Arrow Peak.
It looked like a tailing pile from a mine. Ice inside holds the pile together, Epp said.
As we climbed onto the foot of Vestal Peak, Epp saw more evidence of past glaciers.
"In-bloody-credible," he said, as I climbed over a waist-high ledge, which he believed a glacier had broken off. As the ice masses ground past long ago, they grooved and smoothed rocks, melting at the bottom from the pressure. Then they refroze, binding rocks and popping them off as they passed. "Plucking," Epp said.
Halfway up, we stopped to slip on our harnesses, and I flaked out the rope.
"When you're down below," Epp said, "everything just looks like teeth pointing out."
By now, at 12,808 feet, he had to speak slowly to keep from losing his breath. Up here, he said, the mountain tops, which were all around us, looked even.
"You realize that everything," he said, "was this high once."
And the mountains around Vestal Peak probably were, like a high plain — until the glaciers ground down their flanks, Paul Carrara, who retired from the U.S. Geological Survey after almost four decades, said in an interview after the climb.
In the past 1.7 million years, 17 ice ages have scraped down the Earth, Carrara said. And at the base of the mountain east of Vestal Peak, Trinity Peak, he suspects the last glacier from the most recent big freeze melted a mere 30 years ago.
That freeze would have locked the American West in ice about 30,000 years ago, he said. The glaciers in the San Juan Mountains weren't as fast as the bigger ice sheets at the time in Alaska and western Canada, which could slide several hundred feet a year, but they still ground north and then west a couple of feet annually down the valley we hiked up.
The glaciers carved out that valley sculpting its mountains, but they never crested Vestal Peak.
"Wham Ridge, I'm sure, was probably poking up above the ice surface," he said. "I'm willing to bet the summits over there were never over topped."
Eight and a half hours after we left camp, Epp climbed to the edge of Vestal Peak while I belayed him in from the top. We untied in a safe spot, coiled the rope and walked the last dozen feet to the summit.
"Thirteen thousand, eight hundred and six," I said, reading the altimeter around my neck. It was 58 feet shy.
"Golly," Epp said, looking about at the jagged mountains.
To the west, Arrow Peak's gray and red layers reached into the sky like bent metal. In the south, Mount Eolus loomed amid the other granite needles. And to the east, beyond a glacier-carved basin, were the Trinity peaks, where it is likely the glacial evidence of the last page of these mountains' creation melted away.
It was a perfect chronology.
"It doesn't get better," Epp said.
On the top it was calm and hot, and afternoon clouds mounded at the edges of the blue sky around the peak. But from far away up the valley blew a wind. Oddly, it sounded like the ocean.