Geology, Ecology & Climate Change in the San Juans
Covering about 12,000 square miles, the greater part of Southwestern Colorado and its San Juan Mountains are full of high mountains: 14 peaks exceed 14,000 feet and nearly all the area is above 6,000 feet. These mountains mainly are covered with pine on the lower slopes and spruce and aspen on the higher slopes. Above an altitude of about 12,000 feet only grasses and low bushes grow. The few valleys and bordering foothills below about 8,000 or 9,000 feet are semiarid and have a growth of sagebrush. The grandeur of the mountains is the result of a very long history and a complex series of geological events.
The incredible diversity of canyons, mesas, mountains, plateaus, plains and valleys within and around the 235-mile San Juan Skyway offers visitors a unique geological classroom. The variety of unique landforms that make the Skyway’s scenery so marvelous broadly is the result of straddling the Southern Rocky Mountains and the Colorado Plateau. Visitors are enthralled by dramatic folds in the terrain (geotechnically “anticlinal arches”), basins and glaciated mountains. The Colorado Plateau, which lies within four states, is disrupted by stunning mountains, like the Sleeping Ute Mountains (near Cortez) and the step-like folds of Hogback Mountain (near Durango), but the entire region is most distinguished by its colorful canyons and mesas.
Flying over the San Juans, driving or trekking through them, jagged, sharp-pointed peaks are its most striking and spectacular features. These peaks consist of hard igneous rock. Without getting into geological differences in the mineral composition of hard rocks that, for example, prevail in the San Miguel Mountains, visitors are awed by results in the vicinity of the Skyway like Mountain Wilson and Wilson Peak, and the Needle Mountains. In addition the mountain scenery has been dramatically shaped and deformed by episodic uplift. The rocks of these peaks were formed more than 1.3-1.8 billion years ago (Precambrian era). These rocks are exposed in the steep walls of the spectacular Uncompahgre Canyon south of Ouray. The grand landscape created by these rocks also was shaped by glacial erosion.
We start our clockwise geological and ecological journey around the San Juan Skyway in Ridgway. For centuries the Tabeguache Utes lived in and traveled through what became the Ridgway region. One of the reasons was the presence of what became their “sacred” hot springs – the Orvis Hot Springs, just a few miles south of today’s Ridgway. The story of Ridgway includes the exploration for gold and silver in nearby mountains, Otto Mears acquiring and developing land for the Rio Grande Southern link over the Dallas Divide to Telluride, and the railroad eventually succumbing to competition from trucking. All of this happened before 1956 when the Bureau of Reclamation made its plans for the Ridgway Dam and Reservoir that would have put the town under 100 feet of water. Fortunately the dam was relocated five miles to the north.
Instead we have Ridgway State Park that has a myriad of rock formations, some dating back more than 1.5 billion years, and a wealth of geological treasures. Thirty miles north of the Park, the awe-inspiring Black Canyon of the Gunnison has carved out a deep, narrow canyon through hard schist, gneiss and granite formations. At its deepest point at Painted Wall, the gorge is 2,300 feet deep. South of the Park, volcanic eruption created a thick layer of igneous rock over 35 million years ago. More recently, just 5 million years ago, the era of volcanoes ended and the Ice Ages began. Huge glaciers covered the San Juans and, acting like giant bulldozers, scoured the mountains to carve breathtaking valleys and peaks, including majestic Mount Sneffels (elevation 14,150 feet).
Ridgway itself is built on alluvium deposited by the Uncompahgre River. The soil in and around the town is derived from Mancos Shale which is saline and so fine grained that it does not absorb water easily. Consequently many plant species are not present, which accounts for many bare patches. Interestingly the north-facing steep slopes around Ridgway geologically are better at absorbing moisture, which accounts for the presence of Rocky Mountain juniper and other shrub communities. Nearby and to the south the Uncompahgre Valley also has piñon-juniper.
Every aspect of the environment in the southwest region of Colorado and its mountains is continuously being studied by every category of scientist. These studies are being used by a multiplicity of federal and state agencies, universities and nonprofit organization to make policies and plans for protecting and improving the region’s ecological and geological wonders. All eyes are on the complex impacts of climate change, especially in recent years. Climate change experienced in southwest Colorado and the San Juans over the past few decades certainly has affected the entire environment.
Steadily warming temperatures in spring and summer have been melting the region’s reservoir of snowpack and its water supply more quickly. Warmer temperatures also have been heating up mountain stream water, creating conditions that favor non-native fish and increase trout vulnerability to disease. Colorado’s native trough are becoming confined to only the cleanest and coldest streams, now found mostly at higher elevations. Recent decades have been dominated by drought and, in exceptionally dry periods, watersheds have suffered. And most visibly, drought has been a major factor in the size and severity of fires.
Visitors are attracted to flourishing wildflowers in the San Juans. Understandably they don’t realize that all of the wonderous flowering species are affected in different ways by the timing of snowmelts. Early snowmelt affects early flowering species differently than late flowering species. Differences in the timing of snowmelts can affect all flowering species. For example, early snowmelt reduces soil moisture later in the season and therefore can have negative impacts on both early and late flowering species. Likewise wildlife is affected by changes in snowmelt that alter habitat, food availability, competitors and predators, pests, the timing of hibernation, and other disturbances to the environment. Reductions in snowpack and increased temperatures have led to earlier breeding in amphibian species. Likewise songbirds and other bird species may undergo changes in the timing of migration and breeding. Climate change also can affect fish communities through temperature changes that can affect growth and reproduction.
Although the rate of warming in southwestern Colorado of about 1.1 degree Celsius (2.0 degrees Fahrenheit) in recent decades may not seem like much, it has been greater than anywhere else in the western U.S. or in any other region of the U.S except Alaska. Temperatures in southwestern Colorado are projected to increase by at least as much or more by 2025 and twice that amount by 2050. Both daytime and nighttime temperatures are predicted to increase in summers and winters at all altitudes. Some of the good news in recent climate change scenarios has been a broad consensus that near normal precipitation will occur for most of the year in the future, but still with some level of prevailing uncertainty about future precipitation rates in July and August months. The bad news, however, most clearly has come in the form of forest fires. Everyone breathed a deep sigh of relief when, after 112 days of burning, the Cameron Peak Fire was 100% contained. Although nowhere near the San Juans, this 208,913-acre wildfire — the largest in state history — was indicative of what can happen when forest environments are disrupted by climate change and other factors. Likewise for the state’s second-largest wildfire, the East Troublesome Fire, also recently contained. As for the San Juans, a wildfire burning west of Silverton scorched more than 500 acres of mountains. The Ice Fire, as it came to be known, was the first fire to threaten the town of Silverton in more than 140 years.
For the past few years, southwest Colorado has experienced a prolonged drought. Besides its impact on snowpack and the region’s water sources, trees in the forests have been stressed and are less resistant to fighting threats like the bark beetle. A spruce beetle epidemic in the last decade has been working its way through the Weminuche Wilderness, north toward Silverton and Telluride. Beetle infestations and other climate change factors add more complications to ongoing reforestation efforts. Climate change can influence plant communities directly, by changing temperature and moisture levels, or indirectly by changing the frequency and scale of wildfires or insect and disease outbreaks. The direction, speed and scale of change in plant and tree communities as a result of climate change and human land-use activities are not completely clear. Some predictions say that sagebrush communities will increase in area based on predicted warmer temperatures. Some predictions envision expansion of piñon -juniper and ponderosa pine into sagebrush habitats. Piñon-juniper woodlands have been known to move up and down along various elevations as a result of climate variation, livestock grazing, forestry practices, and success with fire suppression.
Visitors to the San Juans should be grateful for all of the forest health research and reforestation going on in the region. The results of this research should provide reasons for everyone to be somewhat more optimistic about the resiliency of forest ecologies. Conditions may not return to the way things were in past times, but there are continuously promising examples of forest regeneration. For example, on Missionary Ridge, north of Durango, a 2002 wildfire ripped through more than 70,000 acres but 18 years later trees are spreading back throughout the landscape, both through natural means and regeneration projects. Another reason for optimism is all of the new ecology partnerships and working groups that have come together to research and act in innovative ways to solve problematic environmental issues in the San Juan Mountains and elsewhere in Colorado..