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Huerfano: A butte of a county By Rich Stromberg, Mar. 16, 2006 See the photo gallery Author’s note: Geologists have their own vocabulary. I learned more new words in the process of writing this article than I did in an entire year of college. The footnotes should be helpful to clarify these terms in language more common to the layperson, but even this is difficult at times. If you want to skip the geology footnotes, just assume that the word means “some kind of rock” and leave it at that.
Huerfano Butte is the lowest at 6,166 feet[3] sitting at the edge of the eastern plains near the Huerfano River.[4] Legend has it that when the Rocky Mountains marched westward, they left this one little hill behind as an orphan – thus the name Huerfano, which is Spanish for orphan. The butte served as landmark for early Native American, Spanish and other European travelers. The name appears in Spanish records as early as 1818, but was probably named in the late 1700s.
Igneous, but not volcanic “By definition a plug is a plutonic rock that formed underground,” Matthews said. “Don’t call it a volcanic rock until it has poured out onto the ground. None of the buttes are volcanic, but they may have been in the roots of volcanoes.”
“The rationale is that when it vented and reached the surface it would have degassed violently, which would have caused brecciation[9] of rocks around it,” Matthews said. “Since it’s not cleanly cut or broken along margins, this suggests that magma erupted up above. That’s all we can see now. It’s a good indicator that it poured out or blew out way up there.” Matthews said geologists have other evidence that the Goemmer Butte formation was at least a mile underground. The butte sits at 8,043 feet while the ground surface at the time was at least as high as West Spanish Peak, which now stands at 13,626 feet. This is not to say that the ground level was almost 14,000 feet. All that is known is that the formations have risen and fallen through the ages[10] with massive amounts of material eroding away in the process. The ages of the buttes range from 22 million to 27 million years old. Despite what may sound like close ages in the geologic time scale, Matthews said there were three distinct ages and times of intrusion.
Gardner and Goemmer buttes have similar appearances with swirls of brown rock on their steep walls. But amateur geologists should dig deep, at least 10 feet, before drawing conclusions about their origins. “You have to be careful,” Mathews said, “some of the stuff you’re looking at is sedimentary rock baked to the side of the plug. As magma moves up, it bakes and hardens the surrounding material. People think the outside of the dike is the igneous rock when it’s actually the coating. Because the rock is baked, it is as resistant or even more resistant to erosion as the dike.” Hands-on analysis of Huerfano Butte “There are probably three intrusive bodies in Huerfano Butte,” Penn said. “There’s alkali basalt, an east-west trending dike of monzonite through the center and lamprophyre – kamptonite on the east side of the dike. This was a conduit for two very different types of magma – one silica rich and silica poor. These are some of the earliest rocks in the area.” Like Matthews, Penn sees no evidence that Huerfano Butte ever vented to the surface. He said that the presence of breccia along with research by Dave Lindsey strongly suggests that both Gardner and Goemmer buttes did vent, although what we see now are merely the erosional remains. Penn has performed significant argon-argon dating[14] on rock samples collected from Huerfano Butte and the Spanish Peaks region. His data indicates with high confidence that Huerfano Butte is 24 million to 25 million years old. Penn can’t provide a more specific age range for Gardner and Goemmer buttes than Matthews’ 22 million to 27 million year estimate, because no one has performed Ar-Ar dating on samples from these formations. Penn said the minimum age that the Ar-Ar method can accurately determine is around 20 million years. The decay constant is huge with a half-life of 1.25 X 10 to the 9th power years.[15] Penn said that very large sample quantities would be needed for younger samples in order to measure the small decay rate of argon in the rocks.
“Goemmer Butte is made of latite, hornblende[17] and amphibolite[18] mafic enclaves,” Penn said. “It would be good to date. Gardener Butte most definitely vented phenocrysts[19] and quartz - rocks with lots of silicon, even more than the other two Buttes that vented to surface. The rocks are mostly mafic[20] at Huerfano, intermediate at Goemmer and over silicic[21] at Gardner. So is there any particular reason that three major dikes appear in the same county? Was this a hotbed of volcanic activity at one time? “It’s just serendipity that the three dikes showed up there,” Penn said. “There are a lot of things going on. The whole province was very stable[22] for two billion years and was largely undisturbed except by the Rio Grande rift[23] 20 million years ago. The Sangre de Cristo Mountains started to lift only 19 million years ago.[24] What we see now is a very dynamic thing that we think is fixed but it’s not. It’s been going up and down for the last billion years.” Thanks to Sandra Underwood, doctoral candidate in geology at Montana State University who also holds a Ph.D. in chemical engineering from UC Berkley, for her assistance with some of the geology terms in this article. For more information, visit the following Web sites:
www.spanishpeakscolorado.com _____________________________________________________________________________ [1] Despite the fact that many locals massacre this word, the correct pronunciation is where-FAH-no. It is a Spanish word that means orphan. There is no such word as WORE-fuh-no. Doubters are encouraged to consult a dictionary. Hint: it’s a Spanish dictionary. [2] Pronounced BYOOT unless you want to annoy your parents or your teacher, in which case feel free to say BUTT. [3] The 1951 bronze plaque by the highway lists the elevation as 6,150. The USGS topographical map lists it as 6,166 feet. [4] It’s called a river, but it’s really the size of what most people would consider a creek. The Animas, Arkansas, Colorado, and Platte are rivers. [5] He was the son of a Massachusetts governor. The town was named Gardner in 1871. Huerfano County historian Nancy Chistofferson said that the governor sent cantaloupe seeds to his son that became what is known as the Rocky Mountain Melon. Before the town, the site was occupied by the Huerfano Canyon trading post. [6] Pronounced GEM-mer with a hard G. Does this county have some tricky names or what? [7] Spanish for the vein. Pronounced la VAY-tah although many people say VEE-tah. These people are wrong. [8] Pronounced buh-SALT. A fine-grained, dark, igneous rock rich in iron and magnesium composed largely of plagioclase feldspar and pyroxene, whatever the heck they are. [9] Big word. Breccia, which is pronounced BRETCH-ee-ya is an igneous-type rock that includes chunks of other nearby rocks that were broken off when magma flowed through a formation. Check out the Rocky Mountain Magazine article on Silver Mountain for some photos of one type of breccia. Brecciation may not even be a bona-fide word any more than breccification, brecciocity or brecciousness, but geologists made it up out of a need to describe a process. [10] With the relative height of Goemmer Butte to West Spanish Peak staying roughly the same. [11] GAB-ro is a black, coarse-grained, intrusive igneous rock, composed of calcic feldspars and pyroxene. The intrusive equivalent of basalt. Intrusion: An igneous rock body that has forced its way in a molten state into surrounding rock. [12] Temperature zones that run parallel. [13]Devil’s Tower is also known as Bear Lodge where, according to Kiowa legend, seven sisters, escaping the clutches of some hungry bears, jumped onto a small rock. The girls, trapped by the bears, prayed to the rock for aid. The rock answered their prayers by growing to the sky, where the girls became the stars of the Big Dipper. The distinctive columns and lines of the site are attributed to the bears, which clawed at the girls as the rock grew. Numerous Native American cultural ceremonial practices are performed in and around Bear Lodge and many tribal stories and moral lessons are taught by reference to the site. (Source: 41 Idaho L. Rev. 475 ACCOMMODATING NATIVE AMERICAN CULTURAL ACTIVITIES ON FEDERAL PUBLIC LANDS by Erik B. Bluemel.) [14] Techno types who want to learn more details about Ar40-Ar39 dating methods of rocks can read “Guidelines for assessing the reliability of 40Ar/39Ar plateau ages: Application to ages relevant to hotspot tracks” by Ajoy K. Baksi, Department of Geology & Geophysics, Louisiana State University, abaksi@geol.lsu.edu. This method replaces the previous K-Ar method that was accurate when properly controlled, but prone to false results if those controls weren’t strictly followed. Also do a search on Dalrymple, G. B. and Lanphere, M.A. for more information than you’ll ever need to know. [15] That’s 1,250,000,000 or 1.25 billion years for half of the argon to decay into argon-40. The younger age-limit capability of the technique is likely due to accuracy and repeatability of mass spectrometers used to measure the amount of argon-40. The author used to manage a materials analysis laboratory for several years. [16] A little more quartz and feldspar in the rock. [17] Amphibole with aluminum in it. The lower crust of the earth has a lot of amphiboles. [18] Has some feldspar mixed in. [19] When magma is 100 percent liquid, it will cool to a temperature where crystals begin to form. When these crystals become at least .25mm in size they are phenocrysts. Olivine or plagioclase are examples. [20] Remember, this means heavy in iron and magnesium. [21] High in silicon content, like quartz. [22] Volcanic-wise. The continent was still rising and then getting eroded away along with the occasional deposit of an inland sea or two. [23] The Rio Grande Valley from southern Colorado down into New Mexico is slowly pulling apart with the eastern half moving east and the western half moving west. [24] In fact, the Huerfano formation appears on both the east and the west sides of the Sangre de Cristo Mountains.
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Many
people are familiar with Huerfano
It
is not clear that Huerfano Butte is part of any igneous rock
formation that erupted to the surface, despite that its
alkali-basalt
Huerfano
is unlike the other two buttes as most of its rock is
fine-grained gabbro.
As
for differences between the buttes, Penn said that Huerfano
rocks came from lower regions of earth’s crust, while latites