The Dike System, which shoots surrounds the Spanish Peaks is the result of magma filling the cracks on Earth's surface. When the land eroded around 400 large wall-looking landmarks were created. Google Earth image, 12 miles above, taken 9/24/13
The local Ute Indians called them Wahatoya and considered them the sacred “Breasts of the Earth.” Spanish settlers called them Huajatolla and used them as landmarks to guide their travels west. Today, we call them the Spanish Peaks, two distinct mountains just southwest of Pueblo that can be easily seen for miles from all directions.
Rising nearly 7,000 feet above the surrounding terrain and almost as high above sea level as Pikes Peak, the Spanish Peaks are very different from most other mountains in Southern Colorado. While the Wet Mountains and Sangre de Cristos were formed by uplift and traditional plate tectonics, the Spanish Peaks are volcanic in origin.
They formed around 30 million years ago thousands of feet below the earth’s crust, large intrusions of magma or molten rock at 800 to 1,000 degrees Celsius that bubbled up and cut across the existing rock formations of the plains. What we see today are the remnants of two enormous volcanic stocks that have been exposed by millions of years of weather and erosion.
Geologist Chris Rudnick said the Spanish Peaks are one of his favorite features in Southern Colorado.
“One of my favorite things is it’s a double set of volcanic cones. So, they’re right next to each other, and it’s such a spectacular arrangement with the dikes. These dikes are so significant that textbooks use them as examples. The La Veta area is known nationally and internationally for the dike system around the peaks.”
Volcanic dikes form where molten rock has filled cracks in the earth’s surface, and over time as the land erodes away, long ridges of rock remain. The Great Dikes of the Spanish Peaks are one of the most vivid examples of this phenomenon in the world. They radiate from the peaks in all directions like rays of the sun. Some are small and easily measured, while others are miles long and as wide as an eight-lane highway. Scientists have identified over 400 dikes in the areas adjacent to the peaks.
“The San Luis Valley is an ancient rift zone (where two areas of land are moving away from each other), and that caused a lot of volcanic activity in the area,” Rudnick explained. “The region was very active about 35 to 40 million years ago, and some say as recent as 2 million years ago. More land was being created, there were volcanos going off, the air quality would be low, it would’ve definitely been an exciting time to be around.”
“I like to use a scenario to describe what was happening to make it easier to see,” he said. “As the land stretches and rises, it creates weak spots like stretch marks that bleed and leak volcanic material onto the surface. There’s smoke, there’s ash, and sometimes there are objects flying through the air. It’s not as explosive as Mount St. Helens, but it flows out of the ground.”
Though it may be hard for present-day Southern Coloradans to imagine, this scenario paints a very volatile picture of the plains just a few miles south of town. According to Rudnick, there were earthquakes on a daily basis, much like modern-day California, and the climate was subtropical and very warm like the Southern United States. About 5 million years ago, as the climate was drying out, erosion began to increase, uncovering the two peaks and their intricate dike system.
The Spanish Peaks and Great Dikes are some of the easiest geologic formations for people to visit and see firsthand. Driving from Pueblo to La Veta takes about an hour, and then it’s a scenic drive on Highway 12 toward Cuchara that circles around the West Peak and crosses many of the dikes.
“You’re on your way to the San Luis Valley on 160, and just this little 15 minute drive off of 160, down to La Veta and past, gets you right there. You can drive right up to it, and there are some interpretive signs, and sometimes there are mountain sheep up there, too,” Rudnick said. “There was a trip I was on years ago and it was snowing a little bit, and I took photos with the mountain sheep in the snow and the dikes in the background. Sometimes the geology takes a second seat to the animals.”
“There is so much to see around the area of the Spanish Peaks. Out in the valley to the southwest there are volcanic remnants, little cinder cones all over the place,” he said. “And Huerfano Butte is just off I-25 north of Walsenburg. It shows just how close volcanic activity came to Pueblo.”
An alternative way to view the Spanish Peaks is by rail. The Rio Grande Scenic Railroad is based in Alamosa and travels through Fort Garland and the San Luis Valley to La Veta, offering a different perspective of the volcanic countryside.
The Spanish Peaks are just one of many distinctive geologic masterpieces in Colorado, but like all natural wonders, they are slowly eroding and changing with time.
“One thing about geology that I like to emphasize is that it is constantly changing; it’s always something different,” Rudnick said. “Sometimes it happens suddenly like a catastrophe such as a volcanic eruption or a flash flood. But usually, it’s little bits over spans of time, but it’s always, always changing. What we see now, in this shape, won’t be here in 100 years, in 1,000 years and especially in 1 million years. It will be vastly different.”