Stone, Steam and Sand: A Geologic Photo Tour of Southwest Colorado, Part I

The San Juan Mountains

As we traversed Southern Colorado a few weeks ago, my son declared we were in a rainforest. Seeing as how the region is known for arid canyons, pinon trees and cliff houses, I felt the need to correct him. Still, as we crossed the continental divide at Wolf Creek Pass, it was actually raining, giving the dense forest a damp, lush feel. Nearly every rock and towering cliff was covered in moss. We might not have been in an authentic rain forest, but it was a far cry from the desert.

It was easy to see why developers have been eyeing these lands. In a few weeks, the aspen leaves will change in an explosion of color, putting your average Kinkaid painting to shame. Autumn will be followed by blankets of thick snow and throngs of eager skiers. A billionaire from Texas plans to accommodate them by building a resort-class ski village adjacent to the Wolf Creek Ski Area. "Red" McCombs hopes the village will rival other Colorado ski hamlets, like Vail or Breckenridge. The longtime residents of the area aren't too keen on the idea. The Friends of Wolf Creek has the following statement on their website:

Texas billionaire developer "Red" McCombs seeks to construct a city of up to 10,000 people just below the Continental Divide at Wolf Creek Ski Area, one of the snowiest spots in Colorado. The "Village" at Wolf Creek would destroy lush meadows, alpine creeks, unspoiled backcountry recreation opportunities, and one of the most critical wildlife corridors in the Southern Rocky Mountains, harm already established businesses that service Wolf Creek visitors, and dramatically increase traffic on a snowy mountain pass. To build the "Village" though, McCombs needs Forest Service access approval to the 287.5 acre inholding - exchanged in 1987 out of public hands under highly questionable circumstances - across federal lands, as well as Mineral County approval.

Meanwhile, in the valley below, the residents of Pagosa Springs are concerned about a surge of growth and development around town. These days, most of the headlines on the cover of the local newspaper, the Pagosa Sun, concern zoning battles. This week reads: "Final push for 'Big Box' and height regs."

So, what's so special about this area? Take a look:

A valley west of Wolf Creek Pass, at the edge of the San Juan mountains. Highway 160 winds into the distance, alongside the San Juan River. The town of Pagosa Springs lies just over the horizon.

This scene has remained virtually unchanged for decades. Here's a picture of the same area, taken in the 1970s by photographer Don Koch:

I should note, when I found that picture in the Denver Public Library archives, I was rather confused... it was backwards.

Personally, I don't want to see much development in this area. Ski villages and big box stores just don't have the same appeal to me as this landscape. When I looked across the valley, I could see the signs of change-not of commercial development, but millions of years of natural change. Like the battles over ski-bum havens and big box parking lots, it is a history filled with dramatic interactions.

The formation of the Rocky Mountains, overall, was no small thing. As I've described in the past, the Rockies, as we know them today, were formed as the Fallaron plate slipped underneath the North American plate at an unusually shallow angle, causing the land to crumple and fold far beyond the coastal ranges. This was called the Laramide orogeny. While some areas were folded and crumpled, others were stretched thin. Before the Laramide orogeny, the land was marshy and muddy. Layers of sediment accumulated, which under pressure became sandstone and shale. Along the Front Range, near my home, these layers were thrust upwards during the Laramide orogeny. In the San Juans, the ground bulged, and eventually split and cracked, pushing the hot magma beneath towards the surface. Over the course of a few million years, a number of volcanoes erupted across the landscape.

If you take a look at a geologic map of the region, which divides the separate flows of lava and ash from the sedimentary layers with bright, contrasting colors, you can make out the outlines of several ancient volcanoes:

Click here to explore the whole map. The fertile San Luis valley is on the right hand side of the map, while the Rio Grande River and the town of Durango are on the left. (Mesa Verde is just to the west of Durango.) The map is bisected by the continental divide. You can easily make out two major calderas. In the center, a maroon colored blog designates the Creede caldera. Below this, and to the right, is the Summitville caldera, shown by a peach-colored blob. The photographs above show the area in the center of this map, in an area where the volcanic regions overlap:

The photos were taken from the edge of Sheep Mountain, with Jackson Mountain off in the distance. If you cut a section from the map, along the same line of perspective as the photos, you'd have a slice running from the tall peaks of the San Juans, to the town of Pagosa Springs below. The cross section would look something like this:

Note, this cross section isn't to scale at all, nor does it accurately portray the topography of the area. It simply shows the relationship between the layers of rock, showing the relative ages of both the uplifted sediment and the volcanic flows. You can see how layers of ash and lava were deposited atop the sediment from various calderas in the area. The largest of the volcanoes was La Garita. The Fish Canyon tuff, the hardened magma from La Garita, is shown in purple on the map and cross section. The caldera is estimated to be 22 by 50 miles wide, and believed to be the world's largest caldera. The eruption may have choked out life as far away as Kansas.

Long after the ash and lava hardened, the Ice Age brought widespread glaciation to the area. These vast swaths of moving ice carved broad U-shaped valleys into the layers of tuff, before receding back into the mountains. Today, the glaciers are gone, but telltale signs of their path remain. Erratics (large boulders left behind) and other types glacial debris can be found along the slopes of Sheep Mountain. This also left the distinct shape of the valley framed in the pictures above. After the glaciers receded, streams and rivers continued to carve the landscape.

Here, Fall Creek cascades down Treasure Falls, before joining the San Juan River below:

Next, we'll take a look at the signs of volcanism in this area today, with a visit to Pagosa Springs.